Communications device, infrastructure equipment and methods for LTE communication within unused GSM channels

ABSTRACT

A communications device includes a receiver, a transmitter, a controller. The receiver is configured to receive signals representing downlink data from an infrastructure equipment of a wireless communications network via a wireless access interface having a logical baseband frame structure. The transmitter is configured to transmit signals representing uplink data to the infrastructure equipment via the wireless access interface, the logical baseband frame structure being formed from one or more minimum frequency units and one or more time units to form communications resources for allocation by the infrastructure equipment to the communications device. The controller is configured to receive a signal providing an indication of one or more frequency resources available within a host frequency band, to combine the one or more frequency resources within the host frequency band in time and/or frequency to form the one or more of the minimum frequency units of the logical baseband frame structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on PCT filing PCT/EP2015/056155 filedMar. 23, 2015, and claims priority to European Patent Application 14 170435.3, filed in the European Patent Office on May 28, 2014, the entirecontents of each of which being incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to communications devices and methods ofcommunicating data, infrastructure equipment for mobile communicationsnetworks and methods of communicating with communications devices usingmobile communications networks.

The present application claims the priority of EP14158990.3 the contentsof which are herein incorporated by reference.

BACKGROUND OF THE DISCLOSURE

Mobile telecommunication systems, such as those based on the 3GPPdefined UMTS and Long Term Evolution (LTE) architecture, are able tosupport more sophisticated services than simple voice and messagingservices offered by previous generations of mobile telecommunicationsystems. For example, with the improved radio interface and enhanceddata rates provided by LTE systems, a user is able to enjoy high datarate applications such as video streaming and video conferencing onmobile communications devices that would previously only have beenavailable via a fixed line data connection.

The demand to deploy fourth generation networks is therefore strong andthe coverage area of these networks, i.e. geographic locations whereaccess to the networks is possible, is expected to increase rapidly.However, although the coverage and capacity of fourth generationnetworks is expected to significantly exceed those of previousgenerations of communications networks, there are still limitations onnetwork capacity and the geographical areas that can be served by suchnetworks. These limitations may, for example, be particularly relevantin situations in which networks are experiencing high load.

Consequently, there is a demand to deploy fourth generation networks inresources conventionally allocated to preceding mobile communicationssystem such as GSM mobile communications systems. However, although thenetwork operators wish to increase the deployment of fourth generationnetworks, they also wish to maintain the presence of GSM networks forvoice services and low-cost low data rate communications for example. Inorder to address these conflicting requirements it is envisaged thatportions of resources conventionally allocated GSM systems and the likemay be used for the deployment of fourth generation network.

WO 2010091713 addresses a coexistence of two wireless access interfacesoperating in accordance with either a GERAN system or an LTE system bymultiplexing radio frames in time depending on capacity needs of eachsystem. A method is disclosed comprising the steps of predicting adeterministic frequency occupancy of an allocated frequency spectrum ofat least one first wireless access interface for several frames inadvance and allocating at least one frequency band from residual,unoccupied parts of a shared frequency spectrum to the other wirelessaccess interface according to bandwidth requirements. An E-UTRANdescribed in this document occupies a full LTE bandwidth and isscheduled together with GERAN through considering future radio resourcereservations so that E-UTRAN and GERAN do not occupy immediatelyadjacent bands.

Making efficient use of available communications resources represents atechnical problem, for example where spectrum becomes available within afrequency band.

SUMMARY OF THE DISCLOSURE

A communications device comprises a receiver, a transmitter and acontroller. The receiver is configured to receive signals representingdownlink data from an infrastructure equipment of a wirelesscommunications network via a wireless access interface having a logicalbaseband frame structure. The transmitter is configured to transmitsignals representing uplink data to the infrastructure equipment via thewireless access interface, the logical baseband frame structure beingformed from one or more minimum frequency units and one or more timeunits to form communications resources for allocation by theinfrastructure equipment to the communications device. The controller isconfigured to control the transmitter and the receiver to transmit andto receive signals representing the data to and from the infrastructureequipment using the wireless access interface. The controller isconfigured in combination with the transmitter and the receiver toreceive a signal providing an indication of one or more frequencyresources which are available within a host frequency band, to combinethe one or more frequency resources within the host frequency band intime and/or frequency to form the one or more of the minimum frequencyunits of the logical baseband frame structure, and to transmit or toreceive the signals representing the data to or from the infrastructureequipment using the communications resources provided by the one or moreminimum frequency units formed within the host frequency band.

According to the present technique a signal may be transmitted by aninfrastructure equipment of a mobile communications network to assistthe communications device to discover one or more frequency resourceswithin a host frequency band, which can be combined into one or moreminimum frequency resource units for forming a wireless accessinterface. The signal is transmitted by the infrastructure equipment toprovide the communications device with a facility to discover the one ofmore frequency resources within the host frequency band. The signal maybe a discovery signal which is transmitted separately from the frequencyresources or the signal may be transmitted within a first of the one ormore frequency resources, from which one or more other of the frequencyresources may be identified.

The frequency resources may be parts of spectrum previously occupied bya different wireless access interface formed in accordance with adifferent communications network. The frequency resources may be thoughtof and referred to as fractional carriers, because each frequencyresource may form a part of a carrier signal from which a minimum unitof communications resources can be formed by aggregating the fractionalcarriers. Alternatively, the fraction carrier itself may be sufficientto form a minimum unit of communications resource of a wireless accessinterface for a mobile communications network.

According to one example of the present disclosure the host bandincludes one or more unoccupied GSM channels and each of the one or moreminimum frequency units of the second band are positioned in a one ofthe unoccupied GSM channels.

According to another example of the present disclosure a plurality ofthe one or more sub-carriers of at least one of the minimum frequencyunits within the host frequency band are combined for a single time unitto form the communications resources corresponding to the one or moreminimum frequency units.

The combining of resources across a plurality of minimum frequency unitsover a single time unit provides an increased data rate for acommunications device compared to transmissions combining over aplurality of time units. This will therefore provide a communicationssystem which has an improved latency and maximum data rate forindividual communications devices.

Embodiments of the present technique can provide an arrangement for acommunications device to discover the one or more frequency resources,which therefore allows a stand-alone deployment of fractional LTEcarriers in non-contiguous frequency resources without having to resortto cross-carrier scheduling in carrier aggregation.

Various further aspects and embodiments of the disclosure are providedin the appended claims, including but not limited to a communicationssystem and methods of communicating data.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described by way ofexample only with reference to the accompanying drawing in which likeparts are provided with corresponding reference numerals and in which:

FIG. 1 provides a schematic diagram illustrating an example of aconventional mobile telecommunications network;

FIG. 2 provides a schematic diagram illustrating a conventional LTEradio frame;

FIG. 3 provides a schematic diagram illustrating an example of aconventional LTE downlink radio subframe;

FIG. 4 provides a schematic diagram illustrating an example ofconventional LTE uplink subframes;

FIG. 5 provides a schematic diagram of example GSM frequencyallocations;

FIG. 6 provides a schematic diagram of an example GSM frequency resusepattern;

FIG. 7 provides a schematic diagram of an example GSM frequencyallocation;

FIG. 8 provides a schematic representation of an example of frequencyallocations in accordance with the present disclosure;

FIG. 9 provides a schematic representation of an example of frequencyallocations in accordance with the present disclosure;

FIG. 10 provides a schematic representation of an example of frequencyallocations in accordance with the present disclosure;

FIG. 11 provides a schematic representation of an example of frequencyallocations in accordance with the present disclosure;

FIG. 12 provides a schematic representation of an example of frequencyallocations in accordance with the present disclosure;

FIG. 13 provides a schematic representation of an example of frequencyallocations in accordance with the present disclosure;

FIG. 14 provides a schematic representation of an example of frequencyallocations in accordance with the present disclosure;

FIG. 15 provides an example illustration of the use of frequencyallocations in accordance with the present disclosure;

FIG. 16 provides an example illustration representing a discovery signalin accordance with the present disclosure;

FIG. 17 provides an example illustration representing a structure for adiscovery signal in accordance with the present disclosure;

FIG. 18a is an example diagram illustrating an arrangement in which alocation of fraction carriers within a host frequency band areidentified using a linked list type arrangement in accordance with thepresent disclosure in which the first fraction carrier is identifiedusing a discover signal, and FIG. 18b provides a corresponding examplelinked list arrangement in which one of the fractional carriers includesa signal which can be identified by a communications device bysearching;

FIG. 19 provides an example illustration representing a discovery signalin accordance with the present disclosure;

FIG. 20 provides an illustration of an example apparatus for processinga fractional carrier linked list arrangement as for example illustratedin FIGS. 18a and 18b in accordance with the present disclosure;

FIG. 21 provides an example illustration in which a discovery signal inaccordance with the present disclosure directs a communications deviceto a first frequency resource or fractional carrier, which then directsthe communications device to other fractional carriers in time andfrequency;

FIG. 22 provides an example illustration of a discovery signal inaccordance with the present disclosure for detection by low capabilitycommunications devices;

FIG. 23 provides an example of a discovery signal in accordance with thepresent disclosure;

FIG. 24 provides an example of a discovery signal in accordance with thepresent disclosure;

FIG. 25 provides an example of a discovery signal in accordance with thepresent disclosure;

FIG. 26 provides a schematic diagram illustrating a communicationsdevice and a network entity of a mobile telecommunications network

FIG. 27 provides an example OFDM downlink transmitter chain;

FIG. 28 provides an example OFDM downlink receiver chain;

FIG. 29 provides an example OFDM downlink transmitter chain inaccordance with the present disclosure;

FIG. 30 provides an example OFDM downlink transmitter chain inaccordance with the present disclosure;

FIG. 31 provides an example OFDM downlink receiver chain in accordancewith the present disclosure;

FIG. 32 provides an example OFDM downlink receiver chain in accordancewith the present disclosure;

FIG. 33 provides an example SC-FDMA uplink transmitter chain;

FIG. 34 provides an example SC-FDMA uplink receiver chain;

FIG. 35 provides an example SC-FDMA uplink transmitter chain inaccordance with the present disclosure;

FIG. 36 provides an example SC-FDMA uplink receiver chain in accordancewith the present disclosure; and

FIG. 37 provides an example SC-FDMA uplink transmitter chain inaccordance with the present disclosure.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Conventional LTE Communications System

FIG. 1 provides a schematic diagram illustrating some basicfunctionality of a conventional mobile telecommunications network, usingfor example a 3GPP defined UMTS and/or Long Term Evolution (LTE)architecture.

The network includes a plurality of base stations 101 connected to acore network 102, where the base stations may also be referred to asinfrastructure equipment, network elements, network entities, enhancednode Bs (eNodeB) or coordinating entities for example. Each base stationprovides a coverage area 103 (i.e. a cell) within which data can becommunicated to and from communications devices (also referred to asuser terminals, mobile terminals, MT, User equipment, UE and so forth)104 by transmitting and receiving signals representing data across awireless access interface which is provided or associated with theserving base station. Data is transmitted from base stations 101 tocommunications devices 104 within their respective coverage areas 103via a radio downlink. Data is transmitted from communications devices104 to the base stations 101 via a radio uplink. The core network 102routes data to and from the terminal devices 104 via the respective basestations 101 and provides functions such as authentication, mobilitymanagement, charging and so on.

Mobile communications systems such as those arranged in accordance withthe 3GPP defined Long Term Evolution (LTE) architecture use anorthogonal frequency division multiplexing (OFDM) based interface forthe radio downlink (so-called OFDMA) and a single carrier frequencydivision multiple access based interface for the radio uplink (so-calledSC-FDMA).

In LTE systems the wireless access interface of the downlink from aneNodeB to a UE is based upon an orthogonal frequency divisionmultiplexing (OFDM) access radio interface. In an OFDM interface theresources of the available bandwidth are divided in frequency into aplurality of orthogonal subcarriers and data is transmitted in parallelon the plurality of orthogonal subcarriers, where bandwidths between1.25 MHZ and 20 MHz bandwidth may be divided into 128 to 2048 orthogonalsubcarriers for example with between approximately 72 and 1200 of thesubcarriers being occupied and used for data transmission and theremaining subcarriers acting as guard subcarriers. Each occupiedsubcarrier bandwidth may take any value but in LTE it is fixed at 15kHz. The resources of the wireless access interface are also temporallydivided into frames where a frame last 10 ms and is subdivided into 10subframes each with a duration of 1 ms. Each subframe is formed from 14or 16 OFDM symbols and is divided into two slots each of which comprisesix or seven OFDM symbols depending on whether a normal or extendedcyclic prefix is being utilised between OFDM symbols for the reductionof intersymbol interference.

FIG. 2 shows a schematic diagram illustrating an OFDM based LTE downlinkradio frame 201. A primary synchronisation signal (PSS) and a secondarysynchronisation signal (SSS) are transmitted in the first and sixthsub-frames of the LTE radio frame, in frequency division duplex (FDD). Aphysical broadcast channel (PBCH) is transmitted in the first sub-frameof the LTE radio frame. The PSS, SSS and PBCH are discussed in moredetail below.

FIG. 3 is a schematic diagram of a grid which illustrates the structureof an example conventional downlink LTE sub-frame, which may also bereferred to as a time unit or logical baseband frame structure forexample. The sub-frame comprises a predetermined number of “OFDMsymbols”, which are each transmitted over a respective 1/14 ms periodfor example. Each symbol comprises a predetermined number of orthogonalsub-carriers distributed across the bandwidth of the downlink radiocarrier. Here, the horizontal axis represents time while the verticalrepresents frequency.

The example sub-frame shown in FIG. 3 comprises 14 OFDM symbols and 1200sub-carriers spread across a 20 MHz bandwidth, R₃₂₀. The smallestallocation of user data for transmission in LTE is a “physical resourceblock” (PRB) also termed a “resource block” comprising twelvesub-carriers transmitted over one slot (0.5 sub-frame). Each individualbox in the sub-frame grid in FIG. 3 corresponds to twelve sub-carrierstransmitted on one symbol. The resources blocks may also be furtherdivided into resource elements which span one subcarrier for one OFDMsymbol.

FIG. 3 shows in hatching resource allocations for four LTE terminals340, 341, 342, 343. For example, the resource allocation 342 for a firstLTE terminal (UE 1) extends over five blocks of twelve sub-carriers(i.e. 60 sub-carriers), the resource allocation 343 for a second LTEterminal (UE2) extends over six blocks of twelve sub-carriers and so on.

Control channel data is transmitted in a control region 300 (indicatedby dotted-shading in FIG. 3) of the sub-frame comprising the first nsymbols of the sub-frame where n can vary between one and three symbolsfor channel bandwidths of 3 MHz or greater and where n can vary betweentwo and four symbols for channel bandwidths of 1.4 MHz. For the sake ofproviding a concrete example, the following description relates to hostcarriers with a channel bandwidth of 3 MHz or greater so the maximumvalue of n will be 3. The data transmitted in the control region 300includes data transmitted on the physical downlink control channel(PDCCH), the physical control format indicator channel (PCFICH) and thephysical HARQ indicator channel (PHICH).

PDCCH contains control data indicating which sub-carriers on whichsymbols of the sub-frame have been allocated to specific LTE terminals.Thus, the PDCCH data transmitted in the control region 300 of thesub-frame shown in FIG. 3 would indicate that UE1 has been allocated theblock of resources identified by reference numeral 342, that UE2 hasbeen allocated the block of resources identified by reference numeral343, and so on.

PCFICH contains control data indicating the size of the control region(typically between one and three symbols, but four symbols beingcontemplated to support 1.4 MHz channel bandwidth).

PHICH contains HARQ (Hybrid Automatic Request) data indicating whetheror not previously transmitted uplink data has been successfully receivedby the network.

Symbols in the central band 310 of the time-frequency resource grid areused for the transmission of information including the primarysynchronisation signal (PSS), the secondary synchronisation signal (SSS)and the physical broadcast channel (PBCH). This central band 310 istypically 72 sub-carriers wide (corresponding to a transmissionbandwidth of 1.08 MHz). The PSS and SSS are synchronisation signals thatonce detected allow an LTE terminal device to achieve framesynchronisation and determine the cell identity of the eNodeB 101transmitting the downlink signal. The PBCH carries information about thecell, comprising a master information block (MIB) that includesparameters that LTE terminals use to properly access the cell. Datatransmitted to individual LTE terminals on the physical downlink sharedchannel (PDSCH) can be transmitted in other resource elements of thesub-frame. Further explanation of these channels is provided below.

FIG. 3 also shows a region of PDSCH 344 containing system informationand extending over a bandwidth of R₃₄₄. A conventional LTE frame willalso include reference signals which are discussed further below but notshown in FIG. 3 in the interests of clarity.

The number of sub-carriers in an LTE channel can vary depending on theconfiguration of the transmission network. Typically this variation isfrom 72 sub carriers contained within a 1.4 MHz channel bandwidth to1200 sub-carriers contained within a 20 MHz channel bandwidth (asschematically shown in FIG. 3). As is known in the art, data transmittedon the PDCCH, PCFICH and PHICH is typically distributed on thesub-carriers across the entire bandwidth of the sub-frame to provide forfrequency diversity. Therefore a conventional LTE communications devicemust be able to receive the entire channel bandwidth in order to receiveand decode the control region. Further information on the structure andfunctioning of the physical channels of LTE systems can be found in [1].

FIG. 4 provides a simplified schematic diagram of the structure of anuplink of an LTE wireless access interface that may be provided by or inassociation with the eNodeB of FIG. 1. The uplink structure of the LTEwireless access interface may also be referred to as a time unit orlogical baseband frame structure for example in an analogous manner tothe downlink. In LTE networks the uplink wireless access interface isbased upon a single carrier frequency division multiplexing FDM (SC-FDM)interface and downlink and uplink wireless access interfaces may beprovided by frequency division duplexing (FDD) or time divisionduplexing (TDD), where in TDD implementations subframes switch betweenuplink and downlink subframes in accordance with predefined patterns.However, regardless of the form of duplexing used, a common uplink framestructure is utilised. The simplified structure of FIG. 3 illustratessuch an uplink frame in an FDD implementation. A frame 400 is divided into 10 subframes 401 of 1 ms duration where each subframe 401 comprisestwo slots 402 of 0.5 ms duration. Each slot is then formed from sevenOFDM symbols 403 where a cyclic prefix 404 is inserted between eachsymbol in a manner equivalent to that in downlink subframes. In FIG. 3 anormal cyclic prefix is used and therefore there are seven OFDM symbolswithin a subframe, however, if an extended cyclic prefix were to beused, each slot would contain only six OFDM symbols. The resources ofthe uplink subframes are also divided into resource blocks and resourceelements in a similar manner to downlink subframes.

Each uplink subframe may include a plurality of different channels, forexample a physical uplink shared channel (PUSCH) 405, a physical uplinkcontrol channel (PUCCH) 406, and a physical random access channel(PRACH). The physical Uplink Control Channel (PUCCH) may carry controlinformation such as ACK/NACK to the eNodeB for downlink transmissions,scheduling request indicators (SRI) for UEs wishing to be scheduleduplink resources, and feedback of downlink channel state information(CSI) for example. The PUSCH may carry UE uplink data or some uplinkcontrol data. Resources of the PUSCH are granted via PDCCH, such a grantbeing typically triggered by communicating to the network the amount ofdata ready to be transmitted in a buffer at the UE. The PRACH may beused for UE connection initiation and may be scheduled in any of theresources of an uplink frame in accordance with a one of a plurality ofPRACH patterns that may be signalled to UE in downlink signalling suchas system information blocks. As well physical uplink channels, uplinksubframes may also include reference signals. For example, demodulationreference signals (DMRS) 407 and sounding reference signals (SRS) 408may be present in an uplink subframe, where the DMRS occupy the fourthsymbol of a slot in which PUSCH is transmitted and are used for decodingof PUCCH and PUSCH data, and where SRS are used for uplink channelestimation at the eNodeB. Further information on the structure andfunctioning of the physical channels of LTE systems can be found in [1].

In an analogous manner to the resources of the PDSCH, resources of thePUSCH are required to be scheduled or granted by the serving eNodeB.Therefore if data is to be transmitted by a UE, resources of the PUSCHare required to be granted to the UE by the eNodeB, where uplink grantsmay for example be indicated to a UE via DCI conveyed by the PDDCH.Uplink resources may be granted by an eNodeB in a number ofcircumstances, for example a grant may be provided in response to a UEtransmitting a scheduling request or a buffer status report to itsserving eNodeB.

Although similar in structure to downlink subframes, uplink subframeshave a different control structure, in particular the upper 409 andlower 410 subcarriers/frequencies/resource blocks of an uplink subframeare reserved for control signalling rather than the initial symbols of adownlink subframe. Furthermore, although the resource allocationprocedure for the downlink and uplink are relatively similar, the actualstructure of the resources that may be allocated may vary due to thedifferent characteristics of the OFDM and SC-FDM interfaces that areused in the downlink and uplink respectively. In OFDM each subcarrier isindividually modulated and therefore it is not necessary thatfrequency/subcarrier allocations are contiguous. However, in SC-FDMsubcarriers are modulated in combination and therefore if efficient useof the available resources are to be made contiguous frequencyallocations for each UE are preferable.

LTE and GSM Frequency Allocation

In GSM systems, carriers or channels are of a fixed bandwidth of 200 kHzwhere allocated frequency ranges are divided into one or more 200 kHzcarriers. Frequency ranges are also divided into uplink and downlinkbandwidths for frequency division duplex operation. Each carrier withinthe uplink and downlink is divided into eight timeslots in accordancewith a time division multiple access technique, where each communicatingUE is allocated a time slot in each of the uplink and downlinkbandwidths. A plurality of frequency ranges are defined for GSM systems,where for example in the UK three common GSM bands are GSM900, E-GSM900and GSM 1800. However, in other countries different GSM frequency rangesmay be used.

FIG. 5 provides an illustration of the GSM900 (501 502), E-GSM900 (503504) and GSM1800 (506 507) frequency ranges and then divided into uplink(501 503 506) and downlink (502 504 507) frequency ranges where a guardband (505) is present in between the uplink and downlink frequencyallocations. Conventionally, each of the uplink and downlink allocationsare substantially equal in bandwidth such that uplink and downlinkchannel pairs can be provided.

Each pair (uplink and downlink) of GSM carriers is designated anAbsolute Frequency Channel Number (ARFCN) which can be used to identifythe carrier frequencies. Table 1 provides formula for a calculating thefrequency of carrier pairs from their ARFCN number for the threeaforementioned FSM frequency ranges. In Table 1 the uplink frequency isdefined as F1(n) and the downlink frequency Fu(n) where n is the ARFCNnumber.

TABLE 1 GSM900 Fl(n) = 890 + 0.2*n 1 ≤ n ≤ 124 Fu(n) Fu(n) = Fl(n) + 45E-GSM900 Fl(n) = 890 + 0.2*n 0 ≤ n ≤ 124 Fu(n) Fu(n) = Fl(n) = 890 + 975≤ n ≤ 1023 Fl(n) + 45 0.2*(n − 1024) GSM1800 Fl(n) = 1710.2 + 512 ≤ n ≤885 Fu(n) = 0.2*(n − 512) Fl(n) + 95

A characteristic of GSM networks is the implementation of frequencyreuse. When planning networks with limited spectrum available, it isadvantageous if mobile network operators (MNOs) plan the use offrequencies in each cell so that inter-cell interference is minimisedwhilst maximising or increasing capacity. In one common examplesectorisation may be used where a GSM base station may have threesectors, and each sector is assigned one or more frequency channels k.An operator is likely to have a maximum available number of ARFCNchannels, S, depending on the size of the spectrum license it holds. Ifthe S channels are divided among N base stations each of which as threesectors, the number of available channels is

S=3 kN

Those N base stations that together use the complete set of frequenciesavailable constitute a cluster. In GSM networks the decision on thecluster size is a compromise between capacity and interference. A largercluster size, such as 7 or 12, provides larger reuse distance andsmaller inter-cell interference but requires more frequency spectrum toreach the same capacity as smaller cluster sizes.

FIG. 6 provides an illustration of frequency reuse in a GSM network,where the cluster size in four. Each cell 601, 602, 603 is divided intothree sectors 605 to 607 and each cluster comprises cells A, B, C and Dwhich each use different frequencies. Due to the arrangement of thesectors and cell frequency allocation, no two sectors which share acommon frequency are directly adjacent. In the simplified frequencyallocations of FIG. 6, due to a cluster size of four the minimumdistance between sectors sharing a common frequency is one cell, wherefor example cells 601 and 603 which share a frequency band are separatedby cell 602. As mentioned above, a larger cluster size will result in anincreased number of cells/distance between cells which share frequencychannels and therefore reduced inter-cell interference may be achieved.However, additional frequencies will be required. For example, in acluster size of 7 additional frequency resources corresponding tofrequencies used in cells E, F and G may be required.

In recent years MNOs have begun to repurpose the GSM spectrum at 1800MHz into 3G or LTE in order to increase capacity in these systemswhereas the legacy voice and M2M use remains at GSM900 bands. Forexample, in the United Kingdom, LTE has been deployed in at least oneMNOs 1800 MHz band but repurposing of GSM900 band assignments has yet totake place. Consequently, it is likely that most of the GSM900 spectrumassigned to MNOs continues to be deployed in the cellular networkstoday. In light of there being plenty of M2M clients supported by GPRSand GSM900 bands, as well the continuing need to provide basic voicecoverage, the low cost of GSM baseband in a handset and the currentdesirability to avoid the need for countrywide LTE networks, GSM900networks can be expected to remain in use for several years to come.However, due to limited spectrum availability at 1800 MHz, MNOs may alsobe interested in repurposing the portions of the 900 MHz or otheravailable GSM bands when they can shut down some GSM frequencies suchthat the capacity of 3G and LTE networks may be increased.

The repurposing of contiguous portions of frequency bands to LTE may notpose significant problems if the repurposed frequencies are of asufficient size to provide full bandwidth LTE carriers. For example, ifa contiguous portion of frequency of approximately 1.08 MHz or largerwere repurposed an LTE carrier with 72 occupied subcarriers may beprovided using existing LTE procedures. However, repurposing spectrum on900 MHz (and 1800 MHz) bands that have GSM still in operation may not asstraightforward when considering the operational bandwidth of LTEcarriers and the fragmented nature of the available frequencies. In manycases, MNOs are not willing to shut down GSM networks since they providecheap M2M services to existing customers, and also continue to be usedfor voice services. Such problems may be exacerbated by the fact thatcurrent 2G licenses at 900 MHz may not be continuous. For example, inthe Vodafone and Telefonica 17.5 MHz assignments at 900 MHz band in theUnited Kingdom, the license consists of three non-contiguous sections.Example frequency allocations for the UK are shown below in Table 2.

TABLE 2 GSM900 Size of frequencies frequency Operator (uplink) licenseVodafone Limited 880.1-885.1 MHz 5.0 MHz Telefónica UK Limited885.1-890.1 MHz 5.0 MHz Vodafone Limited 890.1-894.7 MHz 4.6 MHzTelefónica UK Limited 894.7-902.3 MHz 5.6 MHz Vodafone Limited902.3-910.1 MHz 7.8 MHz Telefónica UK Limited 910.1-914.9 MHz 4.8 MHz

In some other countries the GSM licenses/frequency allocations are evenmore fragmented and it is may not be possible to find 4 MHz or 5 MHzassignments. For example, the Czech Republic spectrum licenses show apatchwork of narrow assignments among three operators, where an exampleof these allocations are shown in Table 3 below.

TABLE 3 Size of GSM900 frequency Operator frequencies license TelefónicaCzech Republic, 880.1-881.9 MHz 1.8 MHz a.s. Vodafone Czech Republic,881.9-885.4 MHz 3.5 MHz a.s Telefónica Czech Republic, 885.5-886.9 MHz1.4 MHz a.s. T-Mobile Czech Republic, 886.9-889.9 MHz 3.0 MHz a.s.Vodafone Czech Republic, 889.9-894.3 MHz 4.4 MHz a.s T-Mobile CzechRepublic, 894.3-897.1 MHz 2.8 MHz a.s. Telefónica Czech Republic,897.1-899.9 MHz 2.8 MHz a.s. T-Mobile Czech Republic, 899.9-902.1 MHz2.2 MHz a.s. Telefónica Czech Republic, 902.1-904.1 MHz 2.0 MHz a.s.T-Mobile Czech Republic, 904.1-906.1 MHz 2.0 MHz a.s. Telefónica CzechRepublic, 906.1-909.3 MHz 3.2 MHz a.s. T-Mobile Czech Republic,909.3-911.7 MHz 2.4 MHz a.s. Telefónica Czech Republic, 911.7-912.9 MHz1.2 MHz a.s. Vodafone Czech Republic, 912.9-914.9 MHz 2.0 MHz a.s

The use portions of one or more GSM frequencies allocations for theprovision of LTE carriers may be challenging unless approaches such asthe trading of spectrum licenses in order to rearrange spectrumallocations is used. However, frequency trading has not become anestablished practice in areas such as Europe where operators are likelyto consider other means of exploiting their (scattered) resources whichmay result from repurposing GSM frequency resources. Furthermore, inaddition to the fact that GSM frequency allocations for MNOs arefragmented, due to the frequency reuse in GSM, each cell in a cluster ofN cells have different channels in use. Consequently, releasing forexample one GSM channel in a reuse scenario of 6 provides six separatefrequency bands of 200 kHz.

FIG. 7 provides an illustration of frequency use in a GSM system whereBroadcast Control Channel (BCCH) Macro 701 utilises channels 1, 3, 5, 7,9, 11, 13, 15, 17, 19, 21 and 23; Traffic Channel (TCH) 1 7021 utiliseschannels 2, 4, 6, 8, 10, 12, 14 and 16; TCH2 703 utilises channels 18,20, 22, 24, 26 and 28; TCH3 704 utilises channels 25, 30, 32 and 34; andBCCH Micro 705 utilises channels 27, 29, 31, 33, 35 and 37. ReleasingTCH2 (reuse 6) for example would free channels 18, 20, 22, 24, 26 and 28and these channels would be available for repurposing in all the cellsand sectors of the cluster of size six. However, in spite of 1.2 MHz ofspectrum released this way, it may not be possible to fit a conventionalLTE carrier in the non-contiguous group of 200 kHz frequency sub-bandsthat have been freed by releasing TCH 2. Although it may also bepossible to release channels associated with channels other than TCH2,due to the arrangement of frequencies in GSM system any further freedchannels are also unlikely to be contiguous. Consequently, GSM channelsfreed for repurposing are unlikely to be contiguous in frequency andthus unsuitable for the provision of a conventional LTE carrier. Therepurposing of fragmented GSM resources for LTE communications thereforepresents a technical problem of how to utilise non-contiguous frequencyresources of GSM channels for the provision of LTE communications. Aswell as the repurposing of GSM resources for use in LTE systems, a moregeneral technical problem exists of utilising fragmented resources inother communications system which may conventionally utilise contiguousfrequency resources. For example, the use of non-contiguous frequencyresources to transmit and to receive a logical baseband frame structuresuch as that of FIG. 3 which may conventionally be transmitted overcontiguous frequency resources presents a technical problem.

Fractional LTE Carriers

In accordance with a technique disclosed in our co-pending Europeanpatent application EP14158990.3 the contents of which are hereinincorporated by reference, signals of a first communications system thatconventionally operates using a contiguous RF first frequency band maybe divided so that one or more of the divided signals may be transmittedin available, repurposed or unoccupied resources of a second or hostfrequency band, where the second frequency band may include one or moreunoccupied channels of a second communications system that wouldconventionally be too narrow in bandwidth for use in the firstcommunications system. For example, in terms of GSM channels, fractionalcarriers with a bandwidth less then or equal to a GSM channel may bedisposed in each GSM channel. The resources on each of these fractionalcarriers may be used individually to communicate signals representingdata in the first communications system or the resources of thefractional carriers may be used as fragmented resources of the firstcommunications system. In the later case, the resources may be used toform minimum resource or frequency units/blocks that may be individuallyallocated or, alternatively, aggregated to form larger resourcestructures such as logical baseband frames that would conventionally berequired to be transmitted over a contiguous bandwidth larger than achannel or contiguous portions of the second bandwidth.

In one example, the first system may be an OFDM based system such as anLTE system where fractional carriers or candidate carriers formed from apredetermined number of subcarriers are disposed in contiguous ornon-contiguous GSM channels, and resources of these carriers are thenused to form a logical LTE carrier which includes logical basebandframes structures. Although the fractional carriers may be disposed innon-contiguous frequency channels, in LTE baseband the resources of thenon-contiguous frequency channels and the signal conveyed thereon arecombined to form a logical baseband frame of a continuous LTE carrier.Appropriate processing of the signals transmitted and received acrossthe resources of the fractional carriers is then required to logicallydivide and aggregate the signals such that they appear to have beentransmitted across a single conventional LTE carrier and form singlelogical baseband frame. The arrangement of the fractional carriers aswell as the scheduling of data across the fractional carriers may take anumber of forms depending on implementation options chosen. A number ofdifferent approaches to the provision and use of fractional carriers inrepurposed GSM channels for the formation of LTE baseband framestructures and carriers are detailed below.

FIG. 8 provides an illustration showing the aggregation of resources ofrepurposed GSM channels into a logical baseband frame of an LTE carrierwhich has occupied subcarriers spanning 1.08 MHz. In FIG. 8, fractionalcarriers in the GSM channels 18, 20, 22, 24, 26 and 28 801 associatedwith TCH2 are used to provide resources equivalent to a 1.4 MHz LTEcarrier which includes 1.08 MHz in occupied subcarriers. Splitting anLTE carrier constituted from a number of 180 kHz minimum frequency unitsinto its component parts allows the use of each individual 200 kHzchannel independently in the RF domain by disposing each minimumfrequency units in a 200 kHz channel. The example of FIG. 8 considerssix minimum frequency units or resource block bandwidths 802 to 807which contain 12 LTE resource blocks over a 1 ms period, although forsimplicity the LTE logical baseband frame is shown to be formed from sixresources blocks RB1 to RB6 where each contains two LTE resource blocksspanning one 0.5 ms slot each. However, the present technique may applyto any LTE bandwidth that is defined today or potentially in future 3GPPreleases with differing numbers and positioning of GSM channels requiredaccordingly. Likewise, although the fractional carriers of FIG. 8 areshown to be formed from 12 LTE subcarriers, in other example they may beformed from differing numbers.

In FIG. 8, each of the resources blocks RB1 to RB6 are formed fromsignals transmitted across a fractional carrier disposed in one of therepurposed GSM channels. For example, the signals comprising RB1 aretransmitted across the frequencies of GSM channel 18, the signalscomprising RB2 across GSM channel 20 and so forth, and signals formingthe PDCCH are transmitted across substantially all of the fractionalcarriers of the repurposed GSM channels. The signals of each resourceblock that correspond to an LTE subframe (logical baseband frame) aretransmitted across a subcarriers of a fractional carrier over a periodcorresponding to the duration of an LTE subframe such that signals aredivided or fragmented in frequency. As discussed above, the mapping ofsignals transmitted across the fractional carriers of the repurposed GSMchannels to the LTE carrier may take a number of forms, for example thesignals representing the data of each resource block may transmittedover a plurality of fractional carriers simultaneously within a singlesubframe period (frequency fragmentation). Alternatively, the signalsrepresenting data of each resource block may be transmitted sequentiallyacross a single fractional subcarrier over a plurality of subframedurations (time fragmentation or dilation). A further alternative maycombine the two previous approaches such that the signals representingdata of each resource block is transmitted across different fractionalcarriers but staggered over a plurality of subframe periods for example(frequency and time fragmentation). Each of these approaches shall bedescribed in more detail below.

The creation of fractional carriers enables the deployment of LTE intofragmented frequency resources which would not conventionally be able toaccommodate an LTE carrier and thus be unavailable for use by LTEnetworks. The use of fractional carriers may beneficial in scenarioswhere MNOs wish to share existing frequency resources with GSM and LTEnetworks without having to reserve 1 MHz to 2 MHz of contiguous spectrumfor the provision of an LTE carrier. Consequently, MNOs may release anyGSM channels that are available and deploy LTE into these channels,where previously this was not possible. Thus increasing the flexibilityof GSM channel redeployment or repurposing.

Although in FIG. 8 the use of repurposed GSM channels has been describedwith reference to fractional carriers, the use of the repurposed GSMchannels may be described with reference to communications resourceunits or resource units. For example, a vacant GSM channel and thefractional carrier therein may be divided in time into one or moreresource units where the resource units are substantially equal in timeto a subframe and have a bandwidth equal to the minimum LTE frequencyunit that may be allocated (12 subcarriers or 180 kHz for example), suchthat the resources contained therein are substantially similar in extentto those contained in two LTE resource blocks of 180 kHz×1 ms. Aplurality of resource units may then be used to convey the signalsrepresenting the uplink or downlink data of a conventional LTE subframe.Resource units may also be referred to as minimum resource units as theymay be viewed as the minimum resources that a conventional LTE subframemay be broken into for transmission across separate non-contiguousfrequency resources formed from subcarriers in repurposed GSM channels.However, in some examples the minimum resource units may be larger orsmaller in both frequency and time, for instance a minimum resource mayhave dimensions of 180 kHz×0.5 ms so that it corresponds to aconventional LTE resource block rather then two LTE resource blocks.

The combing/aggregation or dividing functionality of the transmitter andreceiver are equivalent to that described above and the signals receivedusing each resource unit are logically aggregated such that theaggregated signal appears to have been transmitted across a singlelogical baseband frame of a conventional LTE carrier. Furthermore,although in the description below various arrangements of fractionalcarriers and signals conveyed thereon are described, the arrangementsmay be also be validly described with reference to resource units.

Whether the use of repurposed GSM channels is viewed in terms offractional carriers of resource units, an indication of the resourceswhich are going to be used transmit to signals using the repurposed GSMchannels is required. In terms of resource units, each availableresource unit within a subframe or frame for example may be allocated anindex number relative to a subframe or frame so that the resource unitsthat are to be used for a transmission may be indicated to a receiverprior to transmission. Alternatively, a plurality of predefined resourceunit patterns may be provided to a communications device such that anindication of a pattern can be provided to a receiver in order toindicate in which resource units signals may be transmitted. As well asthe location of the resource unit, the patterns may also provideinformation on the form of aggregation needed to aggregate the signalsfrom each resource units. In terms of fractional carriers, an indicationof the resources to be used may be provided via an indication of the GSMchannel which is to be used and a timing of transmissions over thefractional carriers of the GSM channels relative to a subframe or frame.

As is discussed in more detail below, a second wireless interfaceestablished via the use of repurposed GSM channels may be provided aloneor in addition to a conventional LTE wireless access interface. In thelater case it may be possible to provide the above discussed indicatorsvia the conventional LTE wireless access interface prior to thetransmission of signals across the repurposed GSM channels.

FIG. 9 provides an illustration of a mapping from resource blocks of anLTE carrier to repurposed GSM channels when signals representing data ofthe resource blocks is transmitted in parallel across a plurality ofminimum frequency units of repurposed GSM channels in the downlink froman eNodeB to a UE. In FIG. 9, at the transmitter the resource blocks 901are treated as a single LTE carrier at baseband but for transmission thesignals of each resource block are mapped to at least one fractionalcarrier in one or more non-contiguous repurposed GSM channels forparallel transmission. At a receiver the signals are received inparallel across the fractional carriers 903 and then combined to form aconventional LTE carrier and frame in baseband such that the use ofnon-contiguous fractional carriers for the transmission of the signalsis transparent to baseband processing at the receiver. The basebandprocessing at the transmitter side in the eNodeB is similar to whatwould take place in a typical implementation, and the baseband frame istreated as six resource blocks constituting a 1.4 MHz carrier. Thechanges in processing are present at the RF front end side where forexample six parallel FFT processes may create the OFDM waveforms of 180kHz and convert them into respective frequency bands to fit into thevacant GSM channels. There may be other means of creating the fractionalcarriers, such as an FFT long enough to cover the whole GSM band, andthe eventual implementation would depend upon complexity and costconsiderations. Consequently, the present technique may be implementedusing a number of alternative transmitter and receiver front end and istherefore independent from the actual IFFT/FFT processing done togenerate and demodulate the fractional carriers.

Although little alteration to the structure of the subframe in basebandis required, the synchronisation channels PSS/SSS may need redesignsince they may be split into separate positions in frequency domainacross one or more fractional carriers and thus not necessarily found inthe same place. It is possible that configuring a UE to attempt combinemultiple N-tuples of fractional carriers in order to find all theconstituent parts of PSS and SSS would too complex and therefore a newcompatible PSS/SSS arrangement may be required or an indication of thelocation of the PSS and SSS relative to the available fractionalcarriers may be provided to the UE.

The use of parallel reception and transmission of signals acrossfractional carriers may lead to increased complexity. For example, toreceive a transmission of the form in FIG. 9, the UE would need to havea receiver RF bandwidth of at least the maximum possible spacing betweenany two fractional carriers that might form the LTE carrier. At a UEthis may lead to a receiver architecture which has an increasedcomplexity, thus leading to increased costs associated with themanufacture of the UE. These disadvantages may be ameliorated byreducing the bandwidth across which signals are transmitted in parallelwhilst still enabling a LTE carrier to be formed from the resources overwhich the signals are transmitted. For example, this may be achieved byas well as utilising resources fragmented in frequency, utilisingresources fragmented in time as shown in FIG. 10.

In FIG. 10, one or more of the signals of the resource blocks of thelogical baseband frame structure or LTE carrier are transmitted in anon-parallel manner across one or more fractional carriers such that thetransmission of the signals forming the data of subframe 904 areeffectively dilated in time. This therefore allows the front end of a UEreceiver to tune a narrower frequency compared to the example of FIG. 9because non-repurposed GSM channels are not included in the tuningbandwidth. For example, in FIG. 10 the signals of the six resourceblocks 1001 to 1006 are transmitted across five adjacent subframes where1003 and 1004 are transmitted in the same subframe because thefractional subcarriers onto which they area mapped are contiguous infrequency. During reception, the UE RF front-end would tune across todifferent fractional carriers in subsequent subframes. Decoding wouldonly proceed after all the signals of each resource block have beenreceived across the fractional carriers and subsequently aggregated.Although the subframes over which the signals of the resource blocks1001 to 1006 are transmitted are illustrated in FIG. 10 as beingconsecutive, they may also be separated in time accordingly to anysuitable pattern.

In another example, in order to maintain a reduced size FFT/IFFTcompared to the arrangement of FIG. 9, signals transmitted acrossfractional carriers which are in close proximity but not contiguous maybe transmitted in parallel if they fall within the bandwidth of theFFT/IFFT. In this manner smaller FFT/IFFTs may be used than required forFIG. 9 whilst stilling allowing for limited instances where signals aretransmitted and received in parallel across non-contiguous fractionalcarriers. For example, if an FFT/IFFT may process subcarriers which havea bandwidth equivalent to approximately 1 MHz, signals on fractionalcarriers positioned in GSM channels 18 and 22 may be receivedsimultaneously instead of conveyed across consecutive subframes.

In FIG. 11, the signals representing data of resource blocks 1101 to1103 are transmitted in consecutive subframes but a gap of a subframe isintroduced before the signals of the resource blocks 1104 to 1106 aretransmitted in consecutive subframes, where the gap may be one or moresubframes and forms a partition between the two sets of transmissions(Set 1 1107 and Set 2 1108). There may also be one or more timepartitions between the transmissions of signals representing data of theresource blocks. Partitioning the time domain transmission may be usedin TDD systems where it may not be possible to fit all the subframes inone continuous DL or UL part of the radio frame. The order of thesubframes in time domain does not have to be identical to the order ofthe fractional carriers in frequency domain, i.e. the fractionalcarriers may be interleaved into a different pattern for transmissionover the air interface. This latter point has the advantage ofseparating frequency-adjacent transmissions in time, amounting to aninterleaving of the PRBs, thus helping to distribute time-domainburst-errors over the frequency domain.

The use of time fragmentation/dilation for the transmission of dataacross fractional carriers may increase the latency of transmissionbecause the minimum time for data to be transmitted increases by thenumber of subframes over which it is fragmented. However, there islittle or no reduction in the overall capacity of the fractionalcarriers because resources of the fractional carriers which area notused may be allocated for use by other UEs. For example, in FIG. 12 aserving eNodeB has scheduled the transmission of signals across theavailable fractional carriers whereby though the signals forming thesubframes of the LTE carriers 1201 to 1203 are fragmented in time,signals for two or more of the subframes are transmitted by the eNodeBin parallel, thus increasing the throughput of the fractional carrierscompared to FIGS. 10 and 11. The arrangement of resource allocations onthe fractional carriers in such a manner therefore allows efficiency ofthe use of the resource of the fractional carriers to be increased. Afurther benefit of this arrangement is that it enables a plurality ofLTE carriers/individual logical baseband frames to be multiplexed onto aset of fractional carriers.

FIG. 13 provides an alternative implementation of the use of fractionalcarriers where the signals forming an LTE carrier are fragmented in timeacross a single fractional carrier whereby signals representing resourceblocks 1301 to 1306 are transmitted consecutively or non-consecutivelyacross the resources of a single repurposed GSM channel, which ischannel 28 in FIG. 13. Using this approach the bandwidth requirements ofa UE's receiver may be reduced as signals 1301 to 1306 are transmittedacross a bandwidth of a single fractional carrier (180 kHz insubcarriers). As before, the signals received in each subframe may thenbe aggregated to form signals an LTE subframe of a LTE carrier whichappears to have been transmitted across a conventional contiguous LTEfrequency allocation. The use of such an arrangement also provides timedilation without the drawback of different OFDM numerology which wouldbe the case if a 6 physical resource block OFDM signal is dilated byreducing subcarrier distance from 15 kHz to one sixth at 2.5 kHz. Alsoin FIG. 13 it is shown that an additional parallel to serial conversionstep 1307 is required, though as described below a number of differentapproaches may be used to fragment the signals representing data of asubframe of a logical LTE carrier for transmission over one or morefractional carriers at the transmitter and aggregate the signalsreceived across fractional carriers.

FIG. 14 provides illustration of the fractional carriers of an LTEuplink where the fractional carriers have been grouped into two clustersin order to constrain the increase in the cubic metric that is likely tooccur due to the fragmentation of the uplink resources. More detail onconstraining the cubic metric can be found in Annex 1. In particular thefractional carriers 1 to 6 have been grouped into two clusters 2501 and2502. The signals from the fractional carriers of each cluster are thenformed into a signal logical carrier 2503.

The use of fractional carriers or resource units described aboveprovides a number of approaches to the repurposing non-contiguous GSMchannels for use in LTE networks. However, in addition to thearrangement of the fractional carriers and the resource units thereon intime and frequency, adapted processing at the front end of thetransmitter and receiver may be required to perform logical aggregationof the signals of each fractional carrier and resource unit such that itappears in baseband that signals which form a logical baseband framehave been transmitted across a conventional LTE carrier. Further detailon the possible approaches to adapted processing at the front end of thetransmitter and receiver can be found in Annex 1.

UE Procedure

The capabilities and capacity advantages associated with the use offractional carrier aggregation may be exploited in a number of differentapproaches. Two such approaches are illustrated in FIG. 14. For example,in a first approach

The UE 1401 is connected to a primary cell (Pcell) using a main LTE band1402 which provides all the synchronisation and RRC signalling.Fractional carriers in a GSM band 1403 are considered as a logicalcomponent carrier in carrier aggregation setup.

The UE 1401 is only connected to the eNodeB with the fractional carriersin a GSM band 1403 which thus constitute Pcell and also providesynchronisation and RRC signalling.

The first option may have a recued complexity because fractional carrierlocations can be indicated in resources of the Pcell and the UE may nothave to perform cell search procedures on fragmented frequency resourceswhere it is not easy to find PSS/SSS. On the other hand, this optionmandates the use of carrier aggregation and therefore the secondapproach may be preferable.

The second option likely requires specification changes onsynchronisation signals which may need optimisation to be more easilydiscovered by a UE. This option does provide for independent and moreflexible deployment on the fractional carrier band however, which mayprovide cost benefits in particular for MTC devices.

The implementation of the second option may be simplified by allowing aUE to utilise fractional carriers only following a handover command froma normal LTE eNodeB. The handover message from the source eNodeB caninclude information used during initial setup on the GSM band. Someessentials would include the frequency location of each fractionalcarrier and if the operation was parallel or serial; in the latter casealso the subframe-to-fraction mapping could be included.

Typically, the arrangement of the frequency location of the fractionswould change very slowly with time since they depend on clearance of GSMsignals. When a re-configuration of the fractional carriers is needed, abroadcast indication of the impeding change can be sent on the existingfractional carriers, and this can include the frequency and/or thearrangement to be used after an indicated point in time. The broadcastnotification could contain the time point itself, or similar to normalLTE system information broadcast, the point in time could be a regularlyoccurring modification boundary.

The use of a handover message may not be suitable in the case where a UEenters an area where a fractional carrier has been deployed but thecurrently-serving eNode B is not aware of the fact, or is not configuredto provide relevant information at handover, or is switching on at ‘coldboot’ and has no serving eNodeB yet. For these cases, some autonomousdiscovery of the fractional carriers may be required.

Discovery

When a UE initially enters a standalone fractional carrier cell it isfirst required to acquire synchronisation. However, the UE may not knowthe fractional carriers, for example the GSM carriers, which can be usedor know which of the fractional carriers transmit a synchronisationsignal. In LTE synchronisation, signals span 72 LTE subcarriers, soshorter versions or differently-designed signals may be needed which maybe contained within a single GSM channel in which a fractional carrieris located. In terms of approaches to discovering the location andorganisation of fractional carriers, a number of possible options exist.For example, possible approaches to fractional carrier discovery or afractional carrier discovery signal that indcaites the fractionalcarriers include:

-   -   The UE searches each GSM carrier to see if it can decode a        fractional carrier discovery signal. This would require        searching potentially many GSM carriers, but gives the eNodeB        increased flexibility.    -   The UE searches a pre-determined subset of the GSM carriers to        determine if it can decode a fractional carrier discovery signal        on any of them, which has been preconfigured for a standalone        case, in which the wireless access interface is provided from        only fractional carriers, as represented in FIG. 15 by the        second approach. In the case where a handover is used, instead        of the handover message giving precise details of the fractional        carrier, a pre-determined subset of GSM carriers could be        indicated, which the receiving fractional carrier discovery        signal can use. The eNodeB operating to provide an LTE interface        using fractional carriers can then move the        discovery/synchronisation signal over time. This may also assist        inter-operator roaming where different network operators will        have different free GSM carriers.    -   The UE may have GSM receiver functionality which allows it to        detect and find active GSM carriers. Any GSM channels that do        not have a GSM signal may constitute a subset of carriers which        the UE could try to decode to search for the discovery signal.    -   The discovery signal might be transmitted in one of the e.g. 6        or more fractional carriers re-purposed from GSM to create the        LTE carrier, or it might be transmitted in an additional GSM        carrier to avoid polluting the LTE resources. For example, six        or more fractional carriers could be re-purposed from GSM to        create the LTE carrier, one of which may carry the discovery        signal.

The fractional carrier discovery signal, or discovery/indication signalas it may also be known, may have the dual purpose of discovery andsynchronisation, or it could provide only discovery since it is likelyto be shorter in length than current LTE synchronisation signals. Inthis case, the discovery signal could give some information on thestructure of the fractional carriers, for example, the GSM carrierswhich can be used within the host frequency band, and any time-domainmapping that is needed. In some examples, the signal may be too small toprovide detailed information and thus such information may be carried insystem information blocks, SIBs, on the whole fractional carrier, whichare transmitted by an eNodeB as part of system broadcast information.Regardless of the mechanism by which discovery signals themselves arediscovered, an efficient method of conveying the required informationwithin the discovery signal i.e. the location of fractionalcarriers/unoccupied GSM bands would be advantageous.

Discovery Signal in Downlink

In accordance with embodiments of the present technique a discoverysignal may be provided using an additional GSM carrier that is dedicatedas the discovery signal or by including the discovery signal as a partof one fractional carrier. Providing a discovery signal on an additionalcarrier would leave the fractional carriers which form the logicalbaseband frame structure unoccupied and thus more closely resemble aconventional LTE frame. However, this would require UEs to receivesignals on an additional fractional carrier which may increase thecomplexity and power consumption at UEs. For instance if six GSMchannels/carriers are used to provide an LTE carrier, seven fractionalcarriers may have to be received. Alternatively, utilising resources inone of the fractional carriers which is used to form the LTE logicalbaseband frame structure would result in the UE only tuning to thenumber of GSM channels which are required to form the logical basebandframe structure. However, the disadvantage of this approach is that theresource of the fractional carriers are utilised to convey the discoverysignal thus reducing the useful data carrying capacity.

According to some examples, a discovery signal could indicate one ormore of the following:

-   -   The number of fractional carriers that constitute the logical        LTE carrier;    -   Whether the fractional carriers are transmitted in parallel or        in serial; or    -   At least the location of the first fractional carrier, and        potentially the locations of all the fractional carriers.

FIG. 16 provides an illustration of an example of a discovery signal4000, where the discovery signal occupies a GSM channel 4002 andincludes an indication of which of the GSM channels the fractionalcarriers 4001 are located or an indication of the structure of thefractional carriers. In practice, an LTE fractional carrier discoverysignal may be provided using 12 subcarriers (i.e. one physical resourceblock). However, Adjacent Channel Leakage Power Ratio (ACLR) concerns orfor other reasons, a discovery signal may be narrower or broader andcould have some waveform other than OFDM. Regardless of the actualwaveform used on the discovery signal, it may require some kind ofsynchronisation structure for the UE to find and lock onto. As analternative to specifying the location of all of the occupied fractionalcarriers or desired fractional carriers, the discovery signal may alsocarry a control signalling field, which indicates where the UE can findat least a subset of or one or more of the fractional carriers. In theabsence of a dedicated channel for the discovery signal, it may beconveyed on a part of one fractional carrier. In the case of an LTEsystem, the system may be pre-configured to embed the discovery signalin the LTE resource block structure so that UEs are able to correctlyreceive and decode the sub-frames, in which it is located.

FIG. 17 provides an illustration of example structures of a fractionalcarrier discovery signal. Discovery signal 4100 illustrates a signalwhich is provided over 12 subcarriers 4101, though this may vary, andincludes a synchronisation portion 4102, a fractional carrier structureportion 4103, a fractional carrier indication portion 4104 andunoccupied resources 4105. The synchronisation portion 4102 may providesynchronisation signals which enable UEs to detect the discovery signaland then decode the information contained therein. The fractionalcarrier structure portion 4103 may contain information on how thesignals on the fractional carriers should be aggregated to form thelogical baseband structure or may include information on the fractionalcarriers organisation in time and/or frequency. The first fractionalcarrier indication portion 4104 may include information on the locationin frequency and time of a first fractional carrier. The firstfractional carrier then may include information of where to findsubsequent fractional carriers in a manner analogous to a linked list.Further detail on such a linked list implementation is given below. Theunoccupied portion 4105 may be used to convey additional signalling andin some examples may not be present if the length of the discoverysignal is shortened or the other portions are enlarged for instance.

A discovery signal 4110 illustrates an example in which a signal may beformed over 12 subcarriers 4111 and may have a synchronisation portion4112 and a fractional carrier structure portion 4113, where theseportions have provide similar signalling/functionality as those ofdiscovery signal 4101. However, in contrast to portion 4104, thefractional carrier location portion 4114 provides the location of all ofthe fractional carriers which are to be utilised by the UE. This allowsa UE to receive the discovery signal and then tune to all the fractionalcarriers immediately. However, mapping the locations of all thefractional carriers on a discovery signal encompassing only 180 kHz maybe resource intensive if done in one subframe. Consequently, alternativeways of managing the mapping of carriers, depending on the latency andoverhead requirements may be beneficial.

Although the discovery signals 4100 and 4110 have been illustrated ascomprising particular portions, in practice they may contain only asubset of these portion or may include additional portions which providefurther signalling information relating to fractional carriers.

FIG. 18a provides an illustration of a process to obtain the location offractional carriers where the locations of the fractional carriers arecontained within a linked list. In such a linked list approach thediscovery signal 4200 points to a first fractional carrier 4201 (whichmay be the first in frequency order for example), the first fractionalcarrier 4001 then points to a second fractional carrier 4202 which againin turn points to the next fractional carrier 4203. Continuing thelinked discovery process finally finishes with the last fractionalcarrier 4204 which indicates that there are no further fractionalcarriers following it. In this manner a discovery signal is required toconvey the location of only a single fractional carrier thus reducingthe size of the discovery signal. The discovery signal may be in thesame subframe as the fractional carrier(s) it specifies or may be in apreceding subframe. Similarly, the fractional carriers that arespecified or which are linked via pointers may be located in the same ordifferent subframes and GSM channels depending whether they are dilatedin time or transmitted in parallel or in serial (consecutively).

FIG. 18b provides an illustration of a process to obtain or discover thelocation of fractional carriers where the locations of the fractionalcarriers are contained within a linked list as in FIG. 18a , but where adedicated discovery signal is not required. The process of FIG. 18b issimilar to that of 18 a where fractional carrier 4201 points tofractional carrier 4202, fractional carrier 4202 points to fractionalcarrier 4203, and fractional carrier 4203 points to fractional carrier4204. However, instead of receiving a discovery signal to obtaininformation on the location of the first fractional carrier 4201, the UEis configured to blindly detect the first fractional carrier 4201. Thismay be achieved for example by introducing a predefined synchronisationsignal into the first fractional carrier which is known to compatibleUEs.

The approaches of FIGS. 18a and 18b may require a means of reading thelinked list component without demodulating the PDCCH and PDSCH which arenot available until the last fractional carrier has been found. FIG. 19illustrates an approach to providing such functionality, where the lastor a specific OFDM symbol 4301 or symbols of a subframe 4300 arereserved for carrying the linked list discovery signals. For in LTEsubframe 4300, which includes a control region 4302 and user plane dataregion (PDSCH) 4303, a linked list discovery field/portion is provideusing the last OFDM symbols of the subframe. In terms of LTE this wouldresult in 12 resource elements (Res) (per sacrificed OFDM symbol perPRB-equivalent frequency resource) each subframe to carry a pointer tothe next fractional carrier. The eNodeB and UEs may know of thenon-PDSCH use of such a specific symbol, the eNodeB would rate-matchPDSCH around the relevant REs and UEs may be aware this was being done.Alternatively, PDSCH could just be punctured, i.e. not rate matched, butthere may be unnecessary since a fractional carrier would not besupporting any legacy UEs which were unaware of the non-PDSCH use of thespecific OFDM symbol. The entire OFDM symbol may not be occupied, andthe specific number of REs would depend on how many bits of informationwere carried by the linked list discovery signals and/or the structureof the signal. In one example 12 subcarriers may be used, i.e. one OFDMsymbol. These subcarriers could constitute e.g. three (3)resource-element groups of four (QPSK) symbols each. This would be 12symbols and 24 bits available for the linked list indicator. There are174 [GSM] channels in 3GPP band 8, so the offset (in GSM channels) fromprevious fractional carrier would be 8 bits maximum (which can cover 256values). Furthermore, eight bits repeated by three would be 24 bits,which can be modulated by QPSK to the 12 resource elements of one OFDMsymbol. Although such indexing capability/capacity may not be requiredin some examples and so smaller offset field may be sufficient. Six bitswould provide 64 values (64×200 kHz=12.8 MHz) and benefits of 4×repetition, but the offset range may be insufficient in some cases.However, the general principle of using a part of the LTE subframephysical resources for a linked list can extend to numerousimplementations depending on whether indexing range or encoding strengthetc. is stressed.

FIG. 20 provides an illustration of an example apparatus that may beused to process and introduce a fractional carrier linked list into asubframe. Firstly, an absolute location or an offset relative to areference carrier or previous fractional carrier is input 4400. Thelocation information is then encoded by an encoder 4401 using anappropriate code, scrambled by a scrambler 4402 using an appropriatescrambling sequence and then modulated by a modulator 4403 onto the OFDMsymbol(s) for introduction into the linked list discovery field 4301.Although, three steps are shown in FIG. 20, in a subset of these stepsmay be used or additional steps may be introduced such as interleavingfor example.

Fractional carriers may be transmitted in N subsequent subframes so thatthe UE is only receiving one or a number of adjacent fractional carriersper subframe, thus reducing the complexity of the receiver. Thediscovery of the time domain pattern may be determined from the order ofthe discovery on constituent fractional carriers. Consequently, the UEmay be required to be informed about whether the fractional carriers areall contained in one subframe duration or across a number of subsequentsubframe durations. Once this information is available for the UE, itmay either

-   -   a) Buffer one subframe across all the GSM carriers and follow        the linked list process to discover all the fractional carriers        in it; or    -   b) Find the first subframe indicated by the discovery signal in        the current subframe, and then read the next fractional carrier        in the following subframe and so on.

FIG. 21 provides an illustration of an implementation where a discoverysignal specifies a location of a first fractional carrier/minimumresource block and then a linked list structure is used to direct the UEto the other fractional carriers/minimum recourse blocks across timeand/or frequency. For example, A UE will firstly receive the discoverysignal 4500 which directs the UE to the fractional carrier 4501.Information conveyed by fractional carrier 4501 then directs the UE tofractional carrier 4502 which in turn directs the UE to fractionalcarrier 4503 which finally directs the UE to fractional carrier 4504.Although in this example and the other linked list examples only fourfractional carriers are linked, any number of fractional carriers may belinked via pointers directed to each other.

Thus in accordance with the present technique the fractional carrierscan then be aggregated to form communications resources corresponding toone or more minimum frequency units which form a wireless accessinterface according to LTE. In LTE the time domain structure may have tobe cell specific since the PDCCH is distributed across multiplesubframes. One subframe duration in time would thus have constituentparts of PDCCHs that belong to actually different subframes of the LTEframe structure. Unless all the UEs follow the same time domain pattern,mapping the PDCCH becomes difficult. This leaves the eNodeB with thedecision of whether it serves all the UEs with fractional carriers sentin one subframe, or all the UEs with a specific time domain pattern. Inthe case of a UE that can only receive one 200 kHz channel at a timesuch as MTC devices for example, it is clear that they cannot operate onthe fractional carriers that multi-PRB UEs are reading unless it tunesto a different carrier in each subframe. Accordingly, this kind of UEmay benefit from the structure where all the N fractional carriersconstituting one subframe follow one another sequentially on a single200 kHz channel (FIG. 13). Such a fractional carrier channel may have tobe independent from the other fractional carriers and thus may berequired to be discovered independently.

According to some examples therefore the frequency resources aredisposed in time and frequency, and the signal or discovery signalprovides an indication of a set of the frequency resources forallocation to reduced capability communications devices (MTC UEs) intime to form the one or more minimum frequency resources for thewireless access interface, in which a bandwidth required to receive oneor more of the set of the frequency resources is reduced. An MTC UE istherefore configured to receive signals representing data within thereduced bandwidth of the set of frequency resources. The set of thefrequency resources for the MTC UEs maybe different from another set ofthe frequency resources which are signalled by the signal to anothertype of communications device.

FIG. 22 provides an illustration of an example solution for thecoexistence of such low capability UEs in a fractional carrierframework. In particular, it is proposed that the discovery signal 4600has two discovery portions or fields: a first fractional carrier portion4603 for pointing at a first fractional carrier 4605 of a multi-carrierdomain, and a single fractional carrier location portion 4604 forpointing at the one, specific fractional carrier 4606 that serves suchsingle-channel UEs. After the discovery has taken place these two typesof UEs exists in mutually exclusive spaces of the GSM channels accessingtheir respective fractional carriers. Other than the two portions 4603and 4604, the discovery signal has a similar structure to those of FIG.19 where portion 4601 is equivalent to portions 4102/4112 and portion4602 is equivalent to portions 4103/4113. Although FIG. 22 provides atime domain multiplexing of fractional carrier location information intoa single discovery signal, other ways of constructing the discoverysignal structure are also possible, such as frequency domainmultiplexing.

In some examples of a linked list implementation, the discovery/pointerindications could each map to e.g. two possible GSM channels, and the UEwould semi-blindly check each of them for containing a valid furtherpointer. Assuming it is not necessary to allow all possible pairs ofpossible next locations, there can be some reduction in the number ofstates to indicate and thus less resources may be taken up withfractional carrier signalling. In order ensure correct functioning ofsuch an approach, a network deploying the approach may ensure that nomore than one of the possible GSM channels indicated does in fact have afractional LTE carrier. For example, if it is required that each of 8fractional carriers are to be identified individually then 3 bits willbe required. However, if pairs of fractional carriers are to beidentified then only 2 bits will be required.

In other examples an ‘extended discovery signal’ may be utilised. Inthis case, the bit-states would be mapped in the specifications tospecific channel offsets from where the discovery signal is found, e.g.state 52 (0011 0100₂) indicates to UE that GSM channels at offsets of 7and 23 are both containing fractional carriers. A further rule may thenestablish that only one of the indicated fractions would hold the nextdiscovery pointer, e.g. the one with the higher relative offset forexample. In some instances, bit states might indicate two channels, asin the foregoing example, others might indicate only one channel, ormore than two channels. Depending on how much deployment flexibility isrequired, this extended discovery signal could have fewer than 8 bitsbut still allow discovery of any fractional carriers, especiallyconsidering the aggregation of the indications over several stages ofthe linked-list. Successive (non-extended) discovery pointers may alsobe able to shrink in bit-size without losing any indexing capability,because there are an increasing number of GSM channels already occupiedand known to the UE as occupied i.e. already been pointed to bydiscovery signals on previous fractional carriers. For example, if thereare three fractional carriers: F0, F1 and F2, the discovery signal in F1may not need to be able to index the locations of F0 or F1 for F2.However, in the 174-channel case, at least 46 fractional carriers wouldto have been signalled or occupied etc. before the next discovery signalrequires 7 as opposed to 8 bits.

A further example of discovery signal structure is illustrated in FIG.23, where the discovery signal portion 4701 of a subframe 4700 includesa discovery signal 4702 and a so called ‘anti-discovery signal’ or‘negative discovery signal’ 4703 which indicates GSM channels which donot contain a fractional carrier or a fractional carrier which isintended for the UE of interest. In this manner the two fields 4702 and4703 provide positive and negative indications of GSM channels in whichfractional carriers are located. In FIG. 23 the anti-discovery signal4703 occupies an additional OFDM symbol, so it can have the same size(and indexing range) as the discovery signal 4702, e.g. 8 bits. Thisallows the indication of 256 combinations of [GSM] channels that do notcontain a next fractional carrier or useful fractional carrier (an‘anti-extended discovery signal). The gradual accumulation ofanti-discovery information or negative indicators excludes an increasingnumber of GSM channels and allows the discovery signals to shrink in theway described above, but more quickly as fewer channels are required tobe able to be identified by the discovery signal. For example, wherediscovery signal Dx and anti-discovery signal Ax are in fractionalcarrier Fx, the example below provide an illustration of the savings interms of bits required for the discovery and anti-discovery fields:

-   -   F0 is discovered in GSM channel 3.    -   A0 has state 24 (0001 1000₂), which specifications map to        anti-discovery of GSM channels 26 through 50 inclusive.    -   D0 indicates an offset of 12 GSM channels (0000 1100₂) to find        F1.    -   F1 is thereby discovered in GSM channel 15.    -   A1 has state 185 (1011 1001₂), which specifications map to        anti-discovery of GSM channels 51 through 75 inclusive.    -   D1 now only needs to indicate 122 potential offsets for F2, and        so can be 7 bits.        Anti-discovery signals mapping to more GSM channels may reduce        the number of bits for the discovery signal faster, and        therefore it may be beneficial if anti-discovery signalling        states map to a relatively large number of channels. There is a        design trade-off between the resources required for discovery        and anti-discovery signals. The anti-discovery also does not        have to be 8 bits long—it may be sufficient to have e.g. 16        mappings to relatively large numbers of GSM channels each, in        which case only 4 bits (6 REs with QPSK) are needed for        anti-discovery. In any particular fractional carrier, the        anti-discovery signal may be not present, and this is true        sooner the more GSM channels are mapped for anti-discovery per        state of the anti-discovery signal because the anti-discovery        signal will comprises fewer bits. In this respect, even freeing        up one LTE resource element could allow transmissions of up to        an additional 6 coded bits per subframe (or even 8 in the case        of 256-QAM in a small cell). As well using discovery and        anti-discovery signals individually, a combination of        anti-discovery signals with extended discovery signals may be an        efficient way to signal fractional carrier structure.

FIG. 24 provides an illustration of a subframe 4800 where discoverysignalling 4801 and anti-discovery 4802 signalling are provided in asame OFDM symbol via frequency multiplexing, i.e. some of thesubcarriers in the final OFDM symbol belong to the discovery signal, andthe others belong to the anti-discovery signal. In this manner theresource occupancy of discovery/anti-discovery is reduced thusincreasing the PDSCH capacity of the subframe. The foregoing unbalancedexample of 4 subcarriers for the anti-discovery signal and 8 subcarriersfor the discovery signal may be appropriate when large contiguoussections of spectrum are indicated by anti-discovery, so that it can beindicated with relatively fewer bits than a discovery signal which mightneed finer resolution to support the needs of diverse mobile networkoperators. The physical resource arrangement of discovery and/oranti-discovery could be provided in advance by specification, or,especially in the case where it is shared within one OFDM symbol,blindly discovered by the UE. The latter case allows per-operator (andper-cell) flexibility at the cost of increasing UE effort.

FIG. 25 provides an illustration of an example approach to fractionalcarrier signalling where a discovery signal 4900 indicates all thefractional carriers/minimum resource blocks 4901 4902 4903 4904 for allGSM channels and over time and frequency. However, in this casemultiplexing all this information to one carrier may require longerframe length. Due to the fact that the deployment of fractional LTEcarriers in the operator's band is static and only rarely changes, alonger latency due to linked list or distributed discovery signallingmay be tolerable as fractional carrier locations are unlikely to changewhilst the discovery signalling is being received. Furthermore, the UEonly has to find the fractional carriers once, after which it willalways find the carriers in the same GSM/frequency channels or they areindicated by system information in handover for example.

Discovery Signal in Uplink

In terms of fractional carriers in the uplink, an LTE UE would have toaccess system information in downlink before it would do any uplinktransmissions. Consequently, the UE will have already obtained knowledgeof the location of fractional carriers and received SIB2 which carriesthe radio resource configuration information the RACH configuration.Therefore, by the time the UE would do random access attempts in theuplink it would thus know the location of each fractional LTE carrierand which PRBs would be used for RACH. Nevertheless, the actual designof the PRACH may need modifications for fractional carrier deployments.

The foregoing approach to the discovery of fractional carriers' locationand organisation has the advantage of allowing stand-alone deployment offractional LTE carriers in non-contiguous frequency resources withouthaving to resort to cross-carrier scheduling in carrier aggregation.Removing the requirement for cross carrier scheduling/carrieraggregation simplifies the process of using fractional carriers, whichin turn enables reduced complexity and reduced capability devices suchas MTC devices to make use of fractional carriers. Consequently, theease with which unoccupied GSM channel may be repurposed is increased aswell as the variety of devices that may be served using fractionalcarriers. Furthermore, with the dedicated discovery signal structure animprovement in the acquisition speed of the fractional LTE carriers maybe obtained because component carriers may be found without having to gothrough each GSM channel at a time for each fractional carrier in orderto assemble them into an LTE carrier.

Example Implementation

FIG. 26 provides a schematic diagram of a UE 2700 and an eNodeB 2710 inwhich examples of the presently disclosed technique may be implemented.The UE includes a transmitter 2701, a receiver 2702 and a controller2703, where the controller is configured to control the receiver 2702 todetect signals representing control data and user data transmitted bythe eNodeB 2710, and to estimate the data conveyed by the signals. Thecontroller 2703 is also configured to control the transmitter 2701 totransmit signals representing uplink control data and user data to theeNodeB. Although in FIG. 26 the UE 2700 is illustrated as comprising aseparate transmitter and receiver, it may instead comprise a transceiverwhich is configured in combination with the controller to implement theaforementioned features and techniques. The controller 2703 may comprisea processor unit which is suitably configured/programmed to provide thedesired functionality described herein using conventionalprogramming/configuration techniques for equipment in wirelesstelecommunications systems. The transmitter 2701, receiver 2702 andcontroller 2703 are schematically shown in FIG. 26 as separate elementsfor ease of representation. However, it will be appreciated that thefunctionality of these units can be provided in various different ways,for example using a single suitably programmed general purpose computer,or suitably configured application-specific integratedcircuit(s)/circuitry, or using a plurality of discretecircuitry/processing elements for providing different elements of thedesired functionality. It will be appreciated the UE 2700 will ingeneral comprise various other elements associated with its operatingfunctionality in accordance with established wireless telecommunicationstechniques (e.g. a power source, possibly a user interface, and soforth).

The eNodeB 2710 includes a transmitter 2711, a receiver 2712 and acontroller 2727, where the controller 2727 is configured to control thetransmitter 2711 to transmit signals representing control data and userdata to UEs within a coverage area such as the UE 2700, thus providing awireless access interface to UEs within the coverage area. Thecontroller 2713 is also configured to control the receiver 2713 todetect signals representing user control and uplink data and estimatethe data conveyed by these signals. Although in FIG. 27 the eNodeB 2710is illustrated as comprising a separate transmitter and receiver, it mayinstead comprise a transceiver which is configured in combination withthe controller to implement the aforementioned features and techniquesat the eNodeB. The controller 2713 may comprise a processor unit whichis suitably configured/programmed to provide the desired functionalitydescribed herein using conventional programming/configuration techniquesfor equipment in wireless telecommunications systems. The transmitter2711, receiver 2712 and controller 2713 are schematically shown in FIG.27 as separate elements for ease of representation. However, it will beappreciated that the functionality of these units can be provided invarious different ways, for example using a single suitably programmedgeneral purpose computer, or suitably configured application-specificintegrated circuit(s)/circuitry, or using a plurality of discretecircuitry/processing elements for providing different elements of thedesired functionality. It will be appreciated the eNodeB 2710 will ingeneral comprise various other elements associated with its operatingfunctionality in accordance with established wireless telecommunicationstechniques. For example, the eNodeB 2710 will in general comprise ascheduling entity responsible for scheduling communications. Thefunctionality of the scheduling entity may, for example, be subsumed bythe controller 2713.

Annex 1

Downlink Processing

The processing of the waveforms/signals used to form the transmissionsacross the fractional carriers can be done in multiple ways, for example

-   -   Distributed OFDM covering all fractional carriers    -   Individual OFDM processing for each fractional carrier    -   Separate processing for each 200 kHz GSM channel.

A typical but simplified OFDM modulation process in the LTE downlink isdepicted in FIG. 27. The modulation apparatus includes a serial toparallel converter unit 1401, an IFFT unit 1402, a parallel serialconverter unit 1403 and a digital to analogue converter unit 1404. Theinput sequence of K symbols a₀, a₁, . . . a_(K-1) is converted into Kparallel streams that each correspond to an LTE subcarrier by the serialto parallel converter unit 1401 and input into the IFFT unit 1402, wherethe parallel stream is padded with zeros in order to reach a power oftwo length for N for which the IFFT unit operates. The output of theIFFT unit is converted back to serial form by the parallel to serialconverter unit 1403 and fed into the digital-to-analogue converter unit1404. The output from the digital to analogue converter unit may then bepassed to further stages in the transmitter chain such as poweramplification, up conversion and frequency filtering for example beforefinal transmission.

FIG. 28 provides an illustration of a conventional but simplified OFDMdemodulation apparatus that may be found in an LTE UE. The structure ofthe demodulation apparatus corresponds to the modulation apparatus ofFIG. 27 but where approximately inverse operations are performed. Thedemodulation apparatus comprises an analogue to digital converter orsampler unit 1501, a serial to parallel converter unit 1502, an FFT unit1503 and a parallel to serial converter unit 1504. The received signalr(t) is sampled by the analogue to digital converter unit 1501 and thenconverted into a plurality of parallel streams by the serial to parallelconverter unit 1402. The parallel streams are then converted into thefrequency domain by the FFT unit 1503 and the output streams of the FFTwhich correspond to the padded zeros of FIG. 27 are discarded. Theremaining data streams are converted into serial by the parallel toserial converter unit 1504 and passed to further processing stages suchas data estimation.

A conventional modulation architecture may be used to form the signalsto be transmitted across the fractional carriers of the repurposed GSMchannels however this may lead to increased demands on the RF front endof a transmitter. For example, the IFFT may be stretched to cover thewhole 3GPP band 8 (GSM900 band of 35 MHz) giving the possibility ofproviding OFDM subcarriers into fractional carriers of that band.Preferably, existing GSM carriers which have not been repurposed shouldbe protected by nulls in the IFFT inputs so that the likelihood thatOFDM subcarriers are superimposed on top of GSM signals is recued. Incurrent LTE specifications the largest channel bandwidth of 20 MHz istypically covered by a size-2048 IFFT size, which covers the 1200subcarriers constituting the 18 MHz transmission bandwidth. The 3GPPband 8 would in extreme case contain 2333 subcarriers, so a size-4096IFFT is of sufficient length to map OFDM subcarriers onto it. In thiscase the IFFT length would be only twice as big as the IFFT used in 20MHz processing. Although the generation of OFDM subcarriers with onelong IFFT through introducing nulls may be more demanding on the RFfront-end, at the eNodeB side one can expect to have linear poweramplifiers which do not require a lot of back-off.

FIG. 29 provides an illustration of a modulation apparatus where theIFFT covers a substantial proportional of the GSM bandwidth and inputscorresponding to GSM channels which have not been repurposed are paddedwith zeros. The serial to parallel converter unit 1601, IFFT unit 1602,parallel to serial converter unit 1603 and digital to analogue converterunit 1604 of FIG. 29 are equivalent to those of FIG. 27. However, thesize of the IFFT may be larger such that it spans to entire GSMfrequency range in which fractional carriers may be deployed.

An alternative to the modulation arrangement of FIG. 29 is to processsignals from each fractional carrier in each repurposed GSM channelindependently in which case each IFFT/FFT would only cover 12 LTEsubcarriers, i.e. one resource block (in practice, it is likely apower-of-2 size (I)FFT would be used, e.g. 16 due to the computationalcomplexity advantages these can afford). Such an arrangement isillustrated in FIG. 30 where the output from the serial to parallelconverter unit 1700 is split between a plurality of IFFT units 1701where the number of IFFTs correspond to the number of fractionalcarriers/repurposed GSM channels. The output from each individual IFFTunit is then input into a corresponding parallel to serial converterunit 1702, delayed by a predetermined duration by delay elements 1703,converted into the analogue domain by the digital to analogue converterunits 1704 and then shifted to the appropriate fractional carrierfrequencies by frequency shifter units 1705. The duration by which thesignals of each branch of the modulator are delayed is given by qP whereP=number of IFFT samples per subframe, and a Z^(−qP) block is a delay ofq subframes and the delay depends on the transmission arrangement of thesignals across the fractional carriers. For instance, in a serialarrangement as illustrated in FIG. 10 for example, each delay elementwill delay the signals by a further qP samples in relation to theprevious delay element. However, if parallel transmission is utilised asillustrated in FIG. 9 then little or no delay will be required. AlthoughFIG. 30 shows six IFFT blocks and frequency shifters, in actual siliconimplementation for serial processing of the transmissions there can beone IFFT unit and one parallel-to-serial unit which are re-used for eachconsecutive buffered subframe data. In hardware terms, one frequencyshifter unit could also be used, although clearly it would have to betuned to each frequency shift in turn.

The use of the modulation arrangement illustrated in FIG. 30 providescomplexity benefits over the arrangement of FIG. 29 due to the reducedsize IFFTs required. The complexity reduction can be illustrated byconsidering the complexity order of an N-point (I)FFT (according to theCooley-Tukey algorithm for example) is O(N log₂ N). Instead of needing4096 points to cover the whole GSM band, instead the implementationrequires one 16-point transform, so the relative complexity is:

$\frac{16\mspace{14mu}\log_{2}16}{4096\mspace{14mu}\log_{2}4096} = {\frac{1}{768}.}$Even in the case that multiple, i.e. 6, parallel 16-point (I)FFTs areused, the relative complexity is:

$\frac{6 \times 16\mspace{14mu}\log_{2}16}{4096\mspace{14mu}\log_{2}4096} = {\frac{1}{128}.}$

The demodulation of OFDM signals distributed across a bandwidth may beperformed in analogous ways to the modulation. For example, thedemodulation may be performed across the whole transmission bandwidth ormay only consider each fractional carrier.

FIG. 31 provides a demodulation arrangement at a UE where a singlestretched FFT extending across the whole bandwidth in which fractionalcarriers may be deployed is used. As in FIG. 28, the received signal issampled by a sampler unit 1801, and converted to a plurality of parallelstreams by a serial to parallel converter unit 1802. The parallelstreams are then transformed into the frequency domain by the FFT unit1803 where the FFT outputs which correspond to GSM channels which havenot been repurposed i.e. where there are no fractional carriers, arediscarded. The remaining parallel streams are then converted into aserial stream by parallel to serial converter unit 1804. As discussedabove with reference to FIG. 29, although this approach provides aconceptually simple approach to receive distributed OFDM signals thatmay occur when using fractional carriers, the computational complexityassociated with a single large FFT is significant and therefore isundesirable at a UE because of the resource constraints normally presentat a UE. Consequently, alternatively a demodulation arrangement of FIG.32 which has multiple chains in a corresponding manner to FIG. 30 may beused.

In FIG. 32, the signals received from each fractional carrier are eachsampled by sampling units 1901 and input into a serial to parallelconverter units 1902. The output from each serial to parallel converterunit 1902 are then input to FFT units 1903, the outputs of which isconverted into a serial stream by parallel to serial converter unit 1904to form a single serial stream that mimics the stream that would beobtained if a single continuous LTE carrier were used instead of an LTEcarrier formed from fractional carriers. As discussed with reference toFIG. 30 in a sequential implementation as illustrated in FIG. 13 only asingle demodulation chain may be needed due to the staggered arrival ofthe signals across the fractional carriers however additional buffer ordelay elements may be required. Although multiple FFTs and serial toparallel converters are required for the structure of FIG. 32, similarcomplexity savings may be achieved compared to the structure of FIG. 31because of the reduced size of the FFT units.

Uplink Processing

An LTE UE is granted uplink resources by an UL resource grant messagecarried by DL PDCCH. In addition to the data allocation that occupiesone or more Physical Resource Blocks of 180 kHz the UE also transmitsPUCCH. The PUCCH occupies the upper and lower resource blocks of thelogical uplink transmission band, which is e.g. 1.4 MHz, 5 MHz or someother typical LTE bandwidth. Accordingly to the present technique, theactual bandwidth between the lowest and highest fractional carriers inUL would be different and dictated by the actual distribution ofunoccupied GSM channels the operator has available. Similarly todownlink, the fractional carrier bands (GSM channels) used by the UE maybe indicated by RRC signalling.

As previously mentioned, the LTE uplink utilises SC-FDMA modulation, orpre-coded OFDM as it is also known, (in the UE) and demodulation (in theeNodeB) in order to reduce the peak-to-average power ratio (PAPR) at theUE so that demands on the amplifier at the UE are reduced compared toOFDM. A simplified diagram of LTE SC-FDMA modulation and demodulationapparatus are depicted in FIGS. 33 and 34 respectively.

In FIG. 33, the data to be transmitted a₀, a₁, . . . a_(K-1) is“pre-coded” using a DFT unit 2001 the outputs of which are input into anIDFT unit 2002 where one or more inputs may be zero padded into order toachieve an input size equal to the IDFT size. A cyclic prefix is thenadded to the time domain signal by a cyclic prefix unit 2003 andresulting digital time domain signal is transformed to the analoguedomain by digital to analogue converter unit 2004 prior to furtherprocessing stages such as amplification.

In FIG. 34, received SC-FDMA LTE signals are sampled by a sampling unit2101 and the cyclic prefix is removed by a cyclic prefix removal unit2102. Once the cyclic prefix has been removed the signal is convertedinto the frequency domain by the DFT unit 2103 and the output samplesthat correspond to the zero padding are discarded. The signals are then“decoded” by the IDFT unit 1204 to form a stream of estimated samplesa₀, a₁, . . . a_(K-1).

In order to generate more than one carrier in uplink, it is once againpossible to use a longer FFT/IFFT length in order to cover the completewidth of the band across which the fractional LTE carriers aregenerated. Introducing nulls into the inputs of the IDFT stage of theSC-FDMA modulator can then be used to create spaces where legacy GSMcarriers would be accommodated.

FIGS. 35 and 36 provide illustrations of an approach where a longer IDFTis used to cover the bandwidth across which the fractional carrier aredisposed for the transmission and reception of LTE SC-FDMA uplinksignals, respectively.

In FIG. 35 the input signals are pre-coded using a DFT unit 2201 andthen transformed by the IDFT unit 2202 where inputs which correspond toGSM channels that have not been repurposed for LTE and fractionalcarriers are padded with zeros. The output of the IDFT unit then has acyclic prefix attached by the cyclic prefix unit 2203 and the resultingsignal is subsequently converted into the analogue domain by the digitalto analogue converter unit 2204.

In FIG. 36 the received signal is sampled by a sampler unit 2301 and thedigital domain signal then has the cyclic prefix removed by the cyclicprefix removal unit 2302. The signal output from unit 2302 is thentransformed by the DFT unit 2303 where the outputs of the DFT whichcorrespond to the non-repurposed GSM channel are discarded. Theremaining samples are then decoded by the IDFT to form a single streamwhich is substantially similar to one that would have been transmittedover a conventional contiguous LTE carrier.

LTE uplink resource allocations originally were in a single cluster butfrom Rel′10 onwards the LTE specifications also allow for multi-clusteruplink transmissions (two clusters of consecutive PRBs). However, inpractice, in order to improve the UE transmitter power amplifierefficiency, the peak-to-average power ratio is preferably kept as low aspossible, which is measured in 3GPP specification by the Cubic Metricvalue. SC-FDMA with one cluster of subcarriers is much more powerefficient than multiple separate uplink waveforms. For the purposes ofMachine Type Communications for example, it is unlikely that high bitrates will be required and therefore that two PRBs in uplink would benecessary. Thus, even in the case of completely fragmented 200 kHz GSMchannels, LTE Rel′10 multi-cluster solution would likely suffice throughproviding two 180 kHz uplink carriers.

The actual processing of the multi-cluster transmission has an impact onthe cubic metric. As depicted in FIG. 37, the UE can be implemented withintegrated processing (option 1) where all the baseband components(digital baseband converters 2401 and digital to analogue converters2402) and radio front-end (up converter and addition unit 2403) areshared with the uplink carriers prior to amplification by poweramplifier 2404. This will introduce a need for power amplifier back-offdue to high cubic metric. Option 2 provides lower cubic metric due toindependent processing for each uplink carrier and only the final poweramplification takes place jointly. This may however increase basebandand RF front-end complexity and cost.

The present technique allows uplink resources to be fragmented into asmany fractional carriers as the downlink. However, the possibledisadvantages associated with fragmented uplink carriers in terms of thecubic metric means that it would be beneficial if there an element ofclustering of fractional carriers is maintained in the uplink.

FIG. 14 provides illustration of the fractional carriers of an LTEuplink where the fractional carriers have been grouped into two clustersin order to constrain the increase in the cubic metric that is likely tooccur due to the fragmentation of the uplink resources. In particularthe fractional carriers 1 to 6 have been grouped into two clusters 2501and 2502. The signals from the fractional carriers of each cluster arethen formed into a signal logical carrier 2503 by the modulation anddemodulation arrangements of FIGS. 35 and 36.

The Physical Random Access Channel (PRACH) in uplink occupies sixphysical resource blocks, i.e. 1.08 MHz. The PRACH configuration isindicated in SIB2 and the UEs transmit PRACH preamble in the samecontiguous PRBs of the logically aggregated uplink channel as they woulddo in the usual LTE band. The preamble is distributed over thefractional carriers over the actual frequency resources and logicallyaggregated by the eNodeB receiver after the receipt of all theconstituent fractional carriers as described above.

In a similar manner to that described with reference to the downlink, ameans to convey information on the allocation of resources of thefractional carriers to the UE may be required for the uplink. This maybe done by providing an explicit indication to the UE from the networkelement of the resources of the fractional carriers that may be used, oralternatively an indication of a particular pattern of allocatedresources of fractional carriers may be provided to a UE via a patternreference indicator for example.

Various further aspects and features of the present invention aredefined in the appended claims and various combinations of the featuresof the dependent claims may be made with those of the independent claimsother than the specific combinations recited for the claim dependency.Modifications may also be made to the embodiments hereinbefore describedwithout departing from the scope of the present invention. For instance,although a feature may appear to be described in connection withparticular embodiments, one skilled in the art would recognise thatvarious features of the described embodiments may be combined inaccordance with the disclosure.

The following numbered clauses define further aspects and features ofthe present technique:

1. A communications device for communicating data, the communicationsdevice comprising

a receiver for receiving signals representing downlink data from aninfrastructure equipment of a wireless communications network via awireless access interface having a logical baseband frame structure,

a transmitter for transmitting signals representing uplink data to theinfrastructure equipment via the wireless access interface, the logicalbaseband frame structure being formed from one or more minimum frequencyunits and one or more time units to form communications resources forallocation by the infrastructure equipment to the communications device,and

a controller for controlling the transmitter and the receiver totransmit and to receive signals representing the data to and from theinfrastructure equipment using the wireless access interface, whereinthe controller is configured in combination with the transmitter and thereceiver

to receive a signal providing an indication of one or more frequencyresources which are available within a host frequency band,

to combine the one or more frequency resources within the host frequencyband in time and/or frequency to form the one or more of the minimumfrequency units of the logical baseband frame structure, and

to transmit or to receive the signals representing the data to or fromthe infrastructure equipment using the communications resources providedby the one or more minimum frequency units formed within the hostfrequency band.

2. A communications device according to clause 1, wherein the signalprovides an indication of a number of the frequency resources within thehost frequency band.

3. A communications device according to clause 2, wherein the discoverysignal provides an indication of whether the frequency resources withinthe host frequency band are available to be combined in time andfrequency.

4. A communications device according to any of clauses 1, 2 or 3,wherein the signal is a discovery signal, which provides an indicationof the one or more frequency resources which are available within thehost frequency band.

5. A communications device according to clause 4, wherein the discoverysignal providing the indication of the one or more frequency resourceswhich are available within the host frequency band is received from acarrier of the host frequency band, which identifies in time andfrequency the one or more fractional carriers within the host frequencyband.

6. A communications device according to any of clauses 1, 2 or 3,wherein the signal is a discovery signal, which provides an indicationof a first of the frequency resources within the host frequency band.

7. A communications device according to clause 1, wherein the controlleris configured in combination with the transmitted and the receiver tosearch the host frequency band for the signal which forms part of afirst of the frequency resources within the host frequency band.

8. A communications device according to clause 6 or 7, wherein the firstfrequency resource includes a signal transmitted within the firstfrequency resource which provides information identifying at least oneother frequency resource.

9. A communications device according to any of clauses 6 to 8, whereineach of the one or more frequency resources includes a signalidentifying one of the other frequency resources as a linked list, andthe controller is configured in combination with the transmitter and thereceiver to detect the one or more frequency resources by detecting eachof the frequency resources from the signals transmitted within each ofthe frequency resources identifying the other frequency resource.

10. A communications device according to any of clauses 1 to 9, whereinthe signal includes a negative discovery signal provides an indicationof one or more frequency resources which are not available within thehost frequency band, and the controller is configured in combinationwith the transmitter and the receiver

to receive the negative discovery signal providing the indication of oneor more frequency resources which are not available within the hostfrequency band to be combined in time and/or frequency to form the oneor more of the minimum frequency units of the logical baseband framestructure, and

to use the signal to identify the one or more frequency resources whichare available within the host frequency band for combining in timeand/or frequency to form the one or more minimum frequency units of thelogical baseband frame structure.

11. A communications device according to clause 10, wherein the signalincludes the discovery signal providing the indication of one or morefrequency resources which are available within the host frequency band,and the negative discovery signal providing the indication of one ormore frequency resources which are not available within the hostfrequency band, and the controller is configured in combination with thetransmitter and the receiver

to use the discovery signal in combination with the negative discoverysignal to identify the one or more frequency resources which areavailable within the host frequency band for combining in time and/orfrequency to form the one or more minimum frequency units of the logicalbaseband frame structure.

12. A communications device according to clause 11, wherein the negativediscovery signal provides an indication of a contiguous section offrequency resources comprising a plurality of frequency resources whichare not available for combining in time and/or frequency to form the oneor more minimum frequency units of the logical baseband frame structure.

13. A communications device according to any of clauses 1 to 12, whereinthe frequency resources are disposed in time and frequency, and thesignal provides an indication of a set of the frequency resources forallocation to reduced capability communications devices in time to formthe one or more minimum frequency resources for the wireless accessinterface, in which a bandwidth required to receive one or more of theset of the frequency resources is reduced, and the controller isconfigured in combination with the receiver to receive signalsrepresenting data within the reduced bandwidth of the set of frequencyresources, the communications device being a reduced capability device.

14. A communications device according to clause 13, wherein the set ofthe frequency resources for the reduced capability devices is differentfrom another set of the frequency resources which are signalled by thesignal to another type of communications device.

15. A communications device according to any of clauses 1 to 12, whereinthe signal includes two discovery fields, a first field for pointing ata first of the available frequency resources, which are allocated to afirst set of the communications devices and a second field for pointingto one of the frequency resources which is allocated to a second set ofcommunications devices.

16. A communications device according to clause 15, wherein thecontroller is configured in combination with the transmitted and thereceiver

to detect the first field of the signal, and

to identify the first frequency resource and the other frequencyresources of the one or more frequency resources, which have beenallocated to the communications device, the communications device beingone of the first set of communications devices, and

to combine the one or more frequency resources identified from the firstfield of the signal to form the one or more of the minimum frequencyunits of the logical baseband frame structure.

17. A communications device according to clause 15, wherein thecontroller is configured in combination with the transmitted and thereceiver

to detect the second field of the signal, and

to identify the frequency resource which has been allocated to thecommunications device, the communications device being one of the secondset of communications devices.

18. A communications device according to clause 15, 16 or 17, whereinthe second set of communications devices are reduced capabilitycommunications devices.

19. A communications device according to clause 1, wherein the signalproviding the indication of the one or more frequency resources whichare available within the host frequency band is received from a carrierof the host frequency band, which identifies in time and frequency theone or more fractional carriers.

20. A method for communicating data to and from a communications device,the method comprising

receiving signals representing downlink data from a infrastructureequipment of a wireless telecommunications system via a wireless accessinterface having a logical baseband frame structure,

transmitting signals representing uplink data to the infrastructureequipment wireless access interface, the logical baseband framestructure being formed from one or more minimum frequency units and oneor more time units to form communications resources for allocation bythe infrastructure equipment to the communications device, and

controlling the transmitter and the receiver to transmit and to receivesignals representing the data to and from the infrastructure equipmentusing the wireless access interface, wherein the method includes

receiving a signal providing an indication of one or more frequencyresources which are available within a host frequency band,

combining the one or more frequency resources of the host frequency bandin time and/or frequency to form communications resources correspondingthe one or more of the minimum frequency units providing the logicalbaseband frame structure, and

transmitting or receiving the signals representing the data to or fromthe infrastructure equipment using the communications resources providedby the one or more minimum frequency units formed within the hostfrequency band.

21. A method according to clause 20, wherein the signal is a discoverysignal which provides an indication of a number of the frequencyresources within the host frequency band.

22. A method according to clause 21, wherein the discovery signalprovides an indication of whether the frequency resources within thehost frequency band are available to be combined in time and frequency.

23. A method according to clause 20, wherein the signal is a discoverysignal, which provides an indication of a first of the frequencyresources within the host frequency band.

24. A method according to any of clauses 20, 21 or 22, wherein thesignal is a discovery signal, which provides an indication of the one ormore frequency resources which are available within the host frequencyband.

25. A method according to clause 20, wherein the receiving a signalproviding an indication of one or more frequency resources which areavailable within a host frequency band, comprises

searching the host frequency band for the signal which forms part of thefirst of the frequency resource within the host frequency band.

REFERENCES

-   [1] LTE for UMTS: OFDMA and SC-FDMA Based Radio Access, Harris Holma    and Antti Toskala, Wiley 2009, ISBN 978-0-470-99401-6.-   [2] WO 2010091713

The following numbered clauses provide further example aspects andfeatures of the present technique:

The invention claimed is:
 1. A communications device for communicatingdata, the communications device comprising circuitry configured toreceive signals representing downlink data from an infrastructureequipment of a wireless communications network via a wireless accessinterface having a logical baseband frame structure; transmit signalsrepresenting uplink data to the infrastructure equipment via thewireless access interface, the logical baseband frame structure beingformed from one or more minimum frequency units and one or more timeunits to predefine one or more minimum resource units in frequency andtime to form communications resources for allocation by theinfrastructure equipment to the communications device; transmit and toreceive signals representing the data to and from the infrastructureequipment using the wireless access interface; receive a signalproviding an indication of two or more frequency resources which areavailable within a host frequency band; combine the two or morefrequency resources within the host frequency band in time and/orfrequency to form the one or more of the minimum resource units of thelogical baseband frame structure such that each of the one or moreminimum resource units includes a plurality of the frequency resourcesin time and/or frequency, wherein the one or more minimum resource unitsformed are produced from logically aggregating a set of fractionalcarriers including a first fractional carrier and a second fractionalcarrier and a third fractional carrier selected from the frequencyresources within the host frequency band, to transmit a respective firstsignal transmission and a second signal transmission and a third signaltransmission, the three fractional carrier transmissions are dilatedtemporally respectively for four milliseconds, each of the fractionalcarriers are formed from a predetermined number of subcarriers; andtransmit or to receive the signals representing the data to or from theinfrastructure equipment using the communications resources provided bythe one or more minimum resource units formed within the host frequencyband; wherein the fractional carriers are repurposed resources of thehost frequency band of a communication system different from acommunication system forming the logical baseband frame structure. 2.The communications device as claimed in claim 1, wherein the signalprovides an indication of a number of the frequency resources within thehost frequency band.
 3. The communications device as claimed in claim 2,wherein the signal is a discovery signal that provides an indication ofwhether the frequency resources within the host frequency band areavailable to be combined in time and frequency, and the discovery signalis received separately from the frequency resources or is receivedwithin a first of the two or more frequency resources.
 4. Thecommunications device as claimed in claims 1, wherein the signal is adiscovery signal, which provides an indication of the two or morefrequency resources which are available within the host frequency band.5. The communications device as claimed in claim 4, wherein thediscovery signal providing the indication of the two or more frequencyresources which are available within the host frequency band is receivedfrom a carrier of the host frequency band, which identifies in time andfrequency the one or more fractional carriers within the host frequencyband.
 6. The communications device as claimed in claim 1, wherein thesignal is a discovery signal, which provides an indication of a first ofthe frequency resources within the host frequency band.
 7. Thecommunications device as claimed in claim 1, wherein the circuitry isconfigured to search the host frequency band for the signal which formspart of a first of the frequency resources within the host frequencyband.
 8. The communications device as claimed in claim 6, wherein thefirst frequency resource includes a signal transmitted within the firstfrequency resource which provides information identifying at least oneother frequency resource.
 9. The communications device as claimed inclaim 6, wherein each of the two or more frequency resources includes asignal identifying one of the other frequency resources as a linkedlist, and the circuitry is configured to detect the two or morefrequency resources by detecting each of the frequency resources fromthe signals transmitted within each of the frequency resourcesidentifying the other frequency resource.
 10. The communications deviceas claimed in claim 1, wherein the signal includes a negative discoverysignal provides an indication of two or more frequency resources whichare not available within the host frequency band, and the circuitry isconfigured to receive the negative discovery signal providing theindication of two or more frequency resources which are not availablewithin the host frequency band to be combined in time and/or frequencyto form the one or more of the minimum resource units of the logicalbaseband frame structure; and to use the signal to identify the two ormore frequency resources which are available within the host frequencyband for combining in time and/or frequency to form the one or moreminimum resource units of the logical baseband frame structure.
 11. Thecommunications device as claimed in claim 10, wherein the signalincludes the discovery signal providing the indication of two or morefrequency resources which are available within the host frequency band,and the negative discovery signal providing the indication of two ormore frequency resources which are not available within the hostfrequency band, and the circuitry is configured to use the discoverysignal in combination with the negative discovery signal to identify thetwo or more frequency resources which are available within the hostfrequency band for combining in time and/or frequency to form the one ormore minimum resource units of the logical baseband frame structure. 12.The communications device as claimed in claim 11, wherein the negativediscovery signal provides an indication of a contiguous section offrequency resources comprising a plurality of frequency resources whichare not available for combining in time and frequency to form the one ormore minimum resource units of the logical baseband frame structure. 13.The communications device as claimed in claim 1, wherein the frequencyresources are disposed in time and frequency, and the signal provides anindication of a set of the frequency resources for allocation to reducedcapability communications devices in time to form the one or moreminimum frequency resources for the wireless access interface, in whicha bandwidth required to receive one or more of the set of the frequencyresources is reduced, and the circuitry is configured to receive signalsrepresenting data within the reduced bandwidth of the set of frequencyresources, the communications device being a reduced capability device.14. The communications device as claimed in claim 13, wherein the set ofthe frequency resources for the reduced capability devices is differentfrom another set of the frequency resources which are signalled by thesignal to another type of communications device.
 15. The communicationsdevice as claimed in claim 1, wherein the signal includes two discoveryfields, a first field for pointing at a first of the available frequencyresources, which are allocated to a first set of the communicationsdevices and a second field for pointing to one of the frequencyresources which is allocated to a second set of communications devices.16. The communications device as claimed in claim 15, wherein thecircuitry is configured to detect the first field of the signal; toidentify the first frequency resource and the other frequency resourcesof the two or more frequency resources, which have been allocated to thecommunications device, the communications device being one of the firstset of communications devices; and to combine the two or more resourcesidentified from the first field of the signal to form the one or more ofthe minimum resource units of the logical baseband frame structure. 17.The communications device as claimed in claim 15, wherein the circuitryis configured to detect the second field of the signal; and to identifythe frequency resource which has been allocated to the communicationsdevice, the communications device being one of the second set ofcommunications devices.
 18. The communications device as claimed inclaim 15, wherein the second set of communications devices are reducedcapability communications devices.
 19. The communications device asclaimed in claim 1, wherein the signal providing the indication of thetwo or more frequency resources which are available within the hostfrequency band is received from a carrier of the host frequency band,which identifies in time and frequency the one or more fractionalcarriers.
 20. The communications device as claimed in claim 1, whereineach resource unit is substantially equal in time to a subframe and hasa bandwidth equal to the minimum allocated LTE frequency unit of one LTEresource block.
 21. The communications device as claimed in claim 1,wherein the three fractional carriers are formed from a same frequencyband.
 22. The communications device as claimed in claim 1, wherein thethree fractional carriers are formed at least two different frequencybands.
 23. A method for communicating data to and from a communicationsdevice, the method comprising receiving signals representing downlinkdata from a infrastructure equipment of a wireless telecommunicationssystem via a wireless access interface having a logical baseband framestructure; transmitting signals representing uplink data to theinfrastructure equipment wireless access interface, the logical basebandframe structure being formed from one or more minimum frequency unitsand one or more time units to predefine one or more minimum resourceunits in frequency and time to form communications resources forallocation by the infrastructure equipment to the communications device;transmitting and receiving signals representing the data to and from theinfrastructure equipment using the wireless access interface; receivinga signal providing an indication of two or more frequency resourceswhich are available within a host frequency band; combining the two ormore frequency resources of the host frequency band in time and/orfrequency to form communications resources corresponding the one or moreof the minimum resource units providing the logical baseband framestructure such that each of the one or more minimum resource unitsincludes a plurality of the frequency resources in time and/orfrequency, wherein the one or more minimum resource units formed areproduced from logically aggregating a set of fractional carriersincluding a first fractional carrier and a second fractional carrier anda third fractional carrier selected from the frequency resources withinthe host frequency band, to transmit a respective first signaltransmission and a second signal transmission and a third signaltransmission, the three fractional carrier transmissions are dilatedtemporally respectively for four milliseconds, each of the fractionalcarriers are formed from a predetermined number of subcarriers; andtransmitting or receiving the signals representing the data to or fromthe infrastructure equipment using the communications resources providedby the one or more minimum resource units formed within the hostfrequency band; wherein the fractional carriers are repurposed resourcesof the host frequency band of a communication system different from acommunication system forming the logical baseband frame structure. 24.The A method as claimed in claim 23, wherein the three fractionalcarriers are formed from a same frequency band.
 25. The method asclaimed in claim 23, wherein the three fractional carriers are formed atleast two different frequency bands.
 26. An infrastructure equipment forforming part of a mobile communications network, the infrastructureequipment comprising circuitry configured to transmit signalsrepresenting downlink data to one or more communications devices of awireless communications network via a wireless access interface having alogical baseband frame structure; receive signals representing uplinkdata to the infrastructure equipment via the wireless access interface,the logical baseband frame structure being formed from one or moreminimum frequency units and one or more time units to predefine one ormore minimum resource units in frequency and time to form communicationsresources for allocation by the infrastructure equipment to thecommunications device, wherein the one or more minimum resource unitsformed are produced from logically aggregating a set of fractionalcarriers including a first fractional carrier and a second fractionalcarrier and a third fractional carrier selected from the frequencyresources within the host frequency band, to transmit a respective firstsignal transmission and a second signal transmission and a third signaltransmission, the three fractional carrier transmissions are dilatedtemporally respectively for four milliseconds, each of the fractionalcarriers are formed from a predetermined number of subcarriers; transmitand receive signals representing the data to and from the one or morecommunications devices using the wireless access interface; and transmita signal providing an indication of two or more frequency resourceswhich are available within a host frequency band, which can be combinedin time and/or frequency to form the one or more of the minimum resourceunits of the logical baseband frame structure such that each of the oneor more minimum resource units includes a plurality of the frequencyresources in time and/or frequency; wherein the fractional carriers arerepurposed resources of the host frequency band of a communicationsystem different from a communication system forming the logicalbaseband frame structure.
 27. The infrastructure equipment as claimed inclaim 26, wherein the three fractional carriers are formed from a samefrequency band.
 28. The infrastructure equipment as claimed in claim 26,wherein the three fractional carriers are formed at least two differentfrequency bands.